asveikau 2 hours ago

> TCP Use-After-Free: CVE-2026-98432 / CVSS 9.8

I know it's customary for HN to edit titles to remove extraneous information, but removing "Linux" here really takes away something useful and relevant. This is a Linux vulnerability. If you're running *BSD or Mac or Windows, not affected.

  • tcdent 2 hours ago

    "TCP stack" versus "Linux TCP stack" is an OOM in terms of relevance.

  • gerdesj 58 minutes ago

    Quite, however it looks quite rare:

    "Why it's urgent: the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection. Anthropic, whose researcher reported it, says its Claude model wrote a working proof-of-concept exploit that runs commands as root on "Linux servers with a multipath TCP listener," with no credentials. Go programs open those listeners by default, per the Go Security Team. See the timeline."

    I don't know of any Linux boxes running a multipath TCP listener in my care and I have quite a few. MP generally implies a router of some sort and the intersections in a Venn diagram continue to get smaller ...

    This is still an issue and must be patched but I think it will be rare, very rare.

peanut-walrus 5 hours ago

Some notes I've got about this:

- MPTCP is not a requirement, it is a generic use-after-free.

- Exploitability over the internet is unlikely, most ISP routers drop packets with IP options fields.

- At least according to Red Hat, dropping packets with IP options yourself helps, but is not a full mitigation.

- Successful exploit requires multiple CPU cores to process packets, so systems with just a single core or packet processing pinned to a single core are not affected.

  • wahern 5 hours ago

    > Exploitability over the internet is unlikely, most ISP routers drop packets with ipoptions fields.

    That doesn't track. Apple iPhones are a major user of MPTCP and they report the majority of requests supporting MPTCP, IIRC 70+%.

    • peanut-walrus 5 hours ago

      MPTCP uses TCP options fields, the vulnerability is in IP options.

  • tptacek 4 hours ago

    Dropping packets with IP options from XDP should be a more complete mitigation (also more performant).

  • lossolo 4 hours ago

    And it takes around an hour to do this in lab setting locally:

    > An enabling property of this race condition is that a lost race only fails the handshake without crashing the whole system, so a determined attacker can retry indefinitely until they succeed. In our proof of concept, it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution

    source: https://www.anthropic.com/research/discovering-vulnerabiliti...

  • pigggg 1 hour ago

    Tragically not enough people drop IP options. I did it in the early 2000s for a very large US network and was glad. There's lots of obvious reasons as they're generally an old school ddos path to knock out routers (get punted to the RE/RP exception path, a good way to bypass some loopback/routing engine acls if folks don't filter it right). Every few years some academics pop up with let's use IP options because we can stuff more bullshit in the datagram - it's always a bad idea.

swinglock 5 hours ago

How are Ubuntu and RHEL not fixed? Few operating systems market themselves more as suitable for servers. What are they doing over there?

  • Shank 5 hours ago

    I’m pretty confused because apparently Anthropic is the group that followed “responsible disclosure” but apparently even though upstream was patched a couple weeks ago, still nothing on either.

  • lakeviewterrace 5 hours ago

    Running regression tests I assume; they can't just YOLO shit like most OSS projects for the exact reason you mention.

    • 1over137 3 hours ago

      It could be that it is more YOLO not patching this ASAP. Maybe better to risk some regressions.

  • Flockster 5 hours ago

    Going by the proxmox forum the fix is already in the sources (proxmox released their kernel based on them a few days ago). But I could not see, if it is already released for the users.

    https://forum.proxmox.com/threads/cve-2026-98432-in-proxmox-...

    • tlamponi 5 hours ago

      Yes, we (Proxmox) included the fix for this in 7.0.14-25, which was initially packaged two weeks ago.

      It went through internal QA and to the test soon after that, then a few days later to the no-subscription repository and as of yesterday morning CET it was cleared for the enterprise one, so it's available on all repos of all Products we got in their current supported releases.

      For kernel updates we where even more conservative in the past, but with the current churn on often quite relevant fixes picked up the pace a bit on moving them along, trying still to balance rolling out fixes fast(er) while not doing that so fast that tricky (hardware/setup specific) regressions don't get caught.

      edit: As this makes the rounds we also released a PSA for it now [0] to make our status here easier to find.

      [0]: https://forum.proxmox.com/threads/proxmox-virtual-environmen...

  • kev009 4 hours ago

    If you read commit logs of, say kernel.org and a distro kernel, and aren't concerned you are blissfully ignorant (and it is worse for the broader userland repos). It's particularly bad when they don't track a kernel.org LTS. Their kernel orgs are pretty lean and this has been the status quo for decades. CVEs of sufficient stature like this will get fixed but majority of other issues slip by unnoticed. LTS is kind of a myth, it trades ABI and API stability for a lot of other issues.

    • icedchai 3 hours ago

      Over the past few months I've started to install newer ubuntu kernels using the mainline PPA. However, it goes long periods of time without getting updates, so it's not really a satisfactory solution. In one case I just built the kernel myself.

      LTS doesn't work if you want immediate fixes like the current environment requires.

    • SwellJoe 2 hours ago

      "Their kernel orgs are pretty lean"

      For years, Red Hat employed more kernel developers than anyone and contributed more. These days they're "only" the fourth largest contributor, after Intel, Google, and Meta, but they are still among the largest corporate contributors.

      If that's a lean kernel org, I don't know what a fat one would look like.

      • kev009 1 hour ago

        My hearsay, from friends and colleagues that work(ed) there, is that the shipped product is not really where you see these "heavy hitters".. a lot of the maintenance happens offshore.

        • lmz 1 hour ago

          Just makes sense that they would put the "heavy hitters" on feature development, not backporting security patches.

    • radlad 2 hours ago

      Unfortunately, as a ZFS on Linux user, LTS is the best way to get continual updates without breaking my system.

      • Gigachad 2 hours ago

        Probably best to not leave any ZFS system connected to the internet then.

  • gadtfly 4 hours ago

    Given the current and rapidly upcoming environment, would that not imply that those are no longer viable choices? As like a fairly urgent emergency consideration?

    If they cannot demonstate being systematically able to adapt towards the required reaction time (minutes? hours?) by almost-comically many orders of magnitude (multiple weeks), and it is only going to get worse, then what other conclusion could there be?

    Like they'll only organizationally adapt when it's far too late (everybody using their shit has already been pwned), and then it'll be an unpracticed emergency adaptation.

  • throw0101d 4 hours ago

    > How are Ubuntu and RHEL not fixed?

    Ubuntu has had kernels in the "proposed" component for several days now if you want to pull it in manually. Not yet pushed to "security" or "updates".

  • 1over137 2 hours ago

    >How are Ubuntu and RHEL not fixed?

    IMNSHO this makes them unfit for purpose. I think this is the nail in the coffin for Ubuntu for me.

    • tln 2 hours ago

      It's not a good look.

      I pulled in from -proposed this time.

      Ubuntu was slow on the brotli / CVE-2026-111497 updates as well.

    • roygbiv2 2 hours ago

      What would you suggest for enterprise use of Linux if RHEL is no longer fit for purpose?

      • linsomniac 13 minutes ago

        I'd be seriously considering Debian or, hear me out, NixOS. We run all our work servers on Ubuntu, but ~6 months ago I switched my workstation to NixOS and I couldn't be happier. I've been following "latest" or whatever they call it, being able to treat the OS package versions like the rest of our software (update the flake.lock file and then burn it in in dev+stg for ~2 weeks before rolling to prod) is pretty attractive.

  • kqgnkqgn 2 hours ago

    It seems particularly crazy for Ubuntu given that Debian released their fix something like a couple weeks ago.

  • xorcist 1 hour ago

    It's one of two things: Either they have found some regression with enterprise customers, or they are not happy with the fix.

    RHEL runs with MP-TCP disabled by default, they initially listed it as Important only to later raise it to Critical.

teekert 3 hours ago

I've been compiling a list of cybersecurity RSS feeds to build a small automation (with oversight from Hermes agent) to ping me (ntfy.sh or just Telegram) when a CVE requires my intervention (matching them to a list of services I run for clients and myself.)

My list (of feeds) is still small, but this CVE did not show up, do any of you have any tips for RSS feeds to use for this purpose?

grey-area 5 hours ago
  • AdrianCX 5 hours ago

    so just block multipath and add the firewall rule from article that drops packets with IPv4 options

    • grey-area 5 hours ago

      Hoping fix will be out soon so we don’t have to.

    • stefangordon 5 hours ago

      Both of which we are finding out are apparently insufficient to mitigate this.

    • SoftTalker 28 minutes ago

      "the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection."

      Is iptables considered an "application" here? I.e. can this bug be triggered before iptables drops the packet?

  • codegeek 4 hours ago

    Interestingly, Ubuntu Priority is set to "High" and not "Critical" which is defined as:

    "A significant problem, typically exploitable for nearly all users in a default installation of Ubuntu. Includes serious remote denial of service, local root privilege escalations, local data theft, and data loss."

Shank 5 hours ago

At least if you’re on Amazon Web Services behind a load balancer you probably aren’t really that impacted enough to spend Halloween patching.

> AWS Web Application Firewall, Application Load Balancer, Classic Load Balancer, TLS Listeners on Network Load Balancer, Cloud Front, API Gateway

> Customers using the above services do not receive TCP connections from untrusted sources directly when following best practices. AWS is applying updates to the underlying infrastructure of these services and no immediate customer action is required if you are using these services. We still recommend customers update their self-managed instances behind these services within the next 30 days.

[0]: https://aws.amazon.com/security/security-bulletins/2026-160-...

  • sebmellen 5 hours ago

    Another reason hyperscaler cloud providers will continue to grow (IMO)!

    • exyi 3 hours ago

      My VPS was auto-updated and restarted more than 14 days ago. The logs have rolled already. Probably October 12 early morning.

      Another reason NixOS will continue to grow :)

    • TuxPowered 3 hours ago

      My FreeBSD loadbalancers block packets with IP Options with default config. It’s not rocket science, no matter how Cloud providers are trying to tell us.

    • mikeweiss 3 hours ago

      Unless they themselves (underlying services) get hacked...

  • gwbas1c 5 hours ago

    I'm more worried about my consumer-grade router.

    • wtch98 4 hours ago

      I blocked packets arriving externally on my firewall with ip-options a couple of days ago. Firewall rule has zero hits, and I've got a very open ISP (andrews+arnold), if I want I can host SMTP, DNS, whatever

  • lysace 3 hours ago

    Note: AWS NLB doesn't terminate TCP for TCP listeners.

    It would be great if they introduced mitigations for this vulnerability though.

  • mlcrypto 3 hours ago

    The timeline says the CVE was reported over 2 weeks ago, so why are the alarms sounding now?

9cb14c1ec0 2 hours ago

I suppose I'm not the only one feeling worn out by this tidal wave of vulnerabilities that I somehow have to keep up to?

  • nikanj 2 hours ago

    The good news is, if you emergency patched your Debian for php2shell, you probably got the new kernel on the same apt run. This time the embargo actually held, and the new kernel was out before the CVE came public

    • Gigachad 2 hours ago

      The only way to survive is to just update everything daily or faster.

      At work we currently have a weekly release schedule but im going to push to speed it up because 1 week is far too long to leave packages out of date.

      • fergonco 1 hour ago

        Then you get exposed to a supply chain attack.

        • treebeard901 8 minutes ago

          If AI is building all the systems and writing all the code, and AI is finding bugs and exploits in existing code and code being generated by AI... With the assumption that any code base scanned in its entirety by the latest frontier cybersecurity focused models is secure... This assumption only holds until a more advanced model is created to find bugs and exploits in the code from the now lesser advanced model... Which means even the code the top of the line model just created was never really secure...

          How does this cycle get broken?? Will people ever be able to be sold the (false idea) that their devices are secure?

          The implications are extensive.

  • rvz 1 hour ago

    Nope. This was just the start.

winwang 4 hours ago

It's okay guys, the authors simply don't know how to write good C. A real C programmer would not have shipped such a basic use-after-free bug. Rust is just a crutch.

  • TOMDM 3 hours ago

    With all the "Claude rewrote X in rust!" posts lately, I'm waiting on the inevitable Linux kernel rewrite post.

    Vibe code aside I feel targeted rewrites are becoming more and more justified.

    • Gigachad 2 hours ago

      I wouldn’t be surprised if we start seeing individual drivers and subsystems move over.

      The Linux maintainers have been extremely conservative with the Rust introduction but after the endless CVE apocalypse they might be more receptive.

  • veltas 1 hour ago

    Counterpoint, more than memory bugs exist, and everything's written in C. You're welcome to rewrite in Rust but you'll create countless bugs that aren't memory bugs that mostly already got fixed in the C version. I can't help but think things like fil-C are the most pragmatic route, despite performance costs, for most people relying on programs written in C.

    • herni 1 hour ago

      This is a dumb argument imo. Critical vulnerabilities are mostly due to memory bugs (and not for a lack of other kinds of bugs). Most people relying on programs written in C (or even C++) should consider plans for migrating to software created with toolchains from this century. You cannot indefinitely carry on this tech debt.

gadtfly 5 hours ago

Everything talks about this in terms of servers, but what about desktop Linux in typical setups? Consumer modems and routers? IoT junk?

  • rwmj 4 hours ago

    IoT devices will get fixes delivered on the 12th of never.

    • gadtfly 4 hours ago

      But are they exploitably vulnerable to this specifically in typical setups?

      • rwmj 4 hours ago

        To be fair probably not as many will be single core and this requires multi-core. As for the thousands of other CVEs though ...

        • telebub 2 hours ago

          Dual or quad core is not that unusual even in very cheap SoCs, but this particular CVE needs a kernel line from this decade. Thousands of other CVEs indeed..

    • RedShift1 4 hours ago

      The security fixed will be installed next tuesday.

  • eterm 4 hours ago

    You should assume your IoT junk is already compromised, that's why your IoT junk runs on a dedicated VLAN.

    • gadtfly 4 hours ago

      Desktop Linux in typical setups? Consumer modems and routers?

    • basilikum 4 hours ago

      What kernel is the router managing these VLANs running?

      • Leonard_of_Q 3 hours ago

        An updated one 'cause you're running a virtual router in a container or VM which gets all the updates your server(s) get.

wiskinator 5 hours ago

> Anthropic says Claude wrote the exploit "after initial prompting," that it runs "arbitrary commands as root, without any credentials or user interaction" on servers with a multipath TCP listener, and that in its proof of concept "it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution."

This is wild. I'm a firmware nerd, not a backend nerd, what percentage of TCP/IP servers are 'multipath'?

Also, since IPv6 isn't affected, wouldn't it be funny if this is what it took to get everyone to switch.

  • dist-epoch 5 hours ago

    My understanding is that an app explicitly needs to open a "multipath" socket. Go 1.24 does that by default, so does Caddy, these would be the big ones.

    • grey-area 5 hours ago

      Your understanding seems to be wrong.

      Every Ubuntu version in the last decade is currently vulnerable.

      https://ubuntu.com/security/CVE-2026-98432

      Patches not yet available. That makes this a big deal.

      This article says that this isn’t app level but is level and can be exploited before requests reach apps.

      • dist-epoch 5 hours ago

        > on servers with a multipath TCP listener

        I was talking about the Anthropic blog post, only Go/Caddy enable multipath TCP listeners by default.

        • grey-area 5 hours ago

          Well somebody is wrong, this blog post says:

          Why it's urgent: the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection.

          It reads like it was LLM generated though so who knows. There is at least a simple mitigation for Golang apps if that is the only concern.

          • dist-epoch 5 hours ago

            Both are correct :)

            Anthropic only exploited multipath TCP, but the bug is deeper and also affects TCP connections, but it looks like this path is harder to exploit, and it's unclear if anybody managed to.

            • grey-area 5 hours ago

              Thanks. Expanding exploits is something LLMs seem pretty good at so I’d expect people to manage a more general exploit soon if not already. Hopefully it’ll be patched before that happens.

  • cataflam 5 hours ago

    > what percentage of TCP/IP servers are 'multipath'?

    no idea, but at least Tailscale and Caddy were opening MPTCP sockets on servers I checked.

marcosscriven 5 hours ago

Can anyone explain how use after free results in a practical exploit?

I ask because I’ve been dabbling in rooting various closed devices at home. I’m finding AI fantastic at finding vulnerabilities statically (from firmware upgrade binaries), but when you then ask it to use it to get root or code execution it just goes in circles.

In the end it usually ends up there’s no exploit it can find, because it can’t actually influence the affected memory in a useful way. This is especially so if that memory is in the heap. On the stack it’s a lot more predictable (especially with OOB writes).

  • kstrauser 5 hours ago

    One example is that you might be able to read what was written there. Here that may mean you could read another process’s packet(s). Imagine they were sending unencrypted passwords, perhaps because it’s in a trusted LAN connection.

  • fguerraz 4 hours ago

    If it’s freed it can be reallocated, so then you have pointers to the same area of memory used for completely different data structures, and this can go very wrong

    • marcosscriven 4 hours ago

      I get the principle - what I struggle to find is concrete examples of how it can practically be used.

      How do you know which pointer (as I say, especially if it’s in the heap)? And I know it can go wrong - but how do you do more than just crash the kernel?

      In OOB writes in a stack variable it’s completely clear to me. For other situations I’d love to find real and clearly explained exploits of past UAF or OOB vulnerabilities.

      • cowlevel 4 hours ago

        Getting the right thing allocated in the right place to exploit a UAF is usually very very tricky. For a defender we just need to know it's probably possible and therefore we patch the bug, but the attacker still has a difficult job to do even already knowing a UAF bug.

        The simplest thing you could try to do is allocate several more of the same type of object and hope one of them lands at the same memory address. For example if you can UAF a web app's user session and keep it open for a long time period (not true in the TCP bug), you might try to wait until an admin happens to log in with their session at the same address, then use their admin session.

        Or you can allocate a lot of something else objects and hope a certain field overlaps, like a function pointer if you can write to it. Like suppose you can get some kind of authentication callback pointer to overlap where your packet sequence number was, maybe you can send a certain number of packets to make it point to the return instruction and skip the authentication.

      • wiml 4 hours ago

        A web search for "exploit chain uaf" found me a few real-world and a few tutorial examples, though I don't know which are good.

        At a high level, though: once you've gotten a new object allocated where the old one was, you now have two different views of the same bit of memory. You use valid operations on one view to put the other one into a corrupted state. For example: in a unixlike kernel, maybe one view has a field containing a function pointer (for method dispatch, essentially). You read that field using the other view, use it to deduce something about the target's memory layout, write a new value to the pointer, then use the field via the first view to cause execution to jump to a location you control.

      • tetha 2 hours ago

        I don't think a UAF on its own allows control hijacking in an exploit. You will need further logic bugs or the ability to legitimately or illegitimately control memory, either via further requests / function calls, OOB writes and such. And it will always be extremely specific to the application vulnerable.

        For example, I remember an exploit workshop around reuse of passwd entries. The vulnerable would validate a passwd entry for a non-root user, use it a bit, and later on free and zero it out for security purposes... except it then looked at the passwd entry again in some conditions. Suddenly, the uid was non-zero at first, and zero later on, so later decisions assumed the user was root.

        In a more concurrent situation, a possible vulnerability was a shared cache of these passwd entries. It wouldn't zero them out anymore, but you could create a race condition of starting requests as user A, and then hammering requests as user B, so you'd end up mixing up the permission contexts of these users. Because the passwd entry that had been released back to the pool was overwritten, and then re-read with the value from another context.

        The necessary line of thinking tends to be very different from thinking about program code regularly.

  • strawberryfarm 4 hours ago

    been doing exactly this lately with camera firmware and yeah the circles thing is real, but im pretty sure its a feedback loop problem, not a model problem

    the model spins because it cant test its own guesses. what fixed it for me was emulating the actual device. qemu with the vendor rootfs, real binaries running, and then every claim becomes checkable: did the daemon actually parse my input, which uid is it under, what does its own log say. once it can check things it stops guessing, getting qemu to actually boot the thing was its own little hell though, took more tries than i want to admit.

    the other thing i learned the hard way: most static findings die on reachability, not on exploit primitives. so i run them in the emulator first and kill the unreachable ones cheap, before spending any time on heap work

    on heap vs stack, i think that intuition is desktop shaped. device userland usually has weak or no mitigations, heap uafs are way more tractable there than youd expect

    • marcosscriven 2 hours ago

      Oh yes definitely seen the reachability problem!

      Good ideas on the QEMU. I guess you’d have to patch the binary if it’s expecting particular hardware etc?

      Not sure what you mean by “desktop shaped”?

      Can you give a concrete example of UAF on heap? I’m learning a bit on how this is done, and eventually recognised the LLM is doing something called heap spray. But that seemed to rely on hoping some object you wrote just happened to get interpreted by some process. And that was the “no, wait, pointer f isn’t y” loops.

    • foltik 2 hours ago

      If you really learned anything you should post your own thoughts, not whatever this lowercased Claudish is.

  • lossolo 3 hours ago

    It goes around in circles because a UAF alone isn't enough in a lot of cases, sometimes you also need a chain (an info leak, read/write primitive etc), a way to defeat ASLR and so on depending on what you are working on and target mitigations. Not all UAFs can be used for RCEs, some can be used only for DoS or for nothing really.

mrob 5 hours ago

>the kernel handed those saved options from the request socket to the new connection without copying them, then freed them immediately when the connection went away, while another CPU could still be reading them to build a handshake reply.

If this requires a multi-core system to exploit, it's good news for most of the consumer routers that will never get updates. Saved by cheap single-core hardware.

  • dist-epoch 5 hours ago

    Those routers probably have 20 other critical un-patched exploits ...

    An entire ecosystem of malware crawling and cohabiting in them.

  • microtonal 5 hours ago

    You would be surprised. A lot of cheap consumer routers are have two or four ARM cores. The bigger issue is that they are typically running a kernel from the stone age (< 6.0.0). Sometimes a still-supported LTS kernel like 5.10 or 5.15, but then they stopped at an old patch level.

    Heck, apparently even the new Unifi UCG Fiber is running 5.4.213 (September 2022), but maybe they backport some fixes?

    [1] https://community.ui.com/releases/dd0283dc-bf71-4140-ae1d-c1...

    • FredFS456 3 hours ago

      Note that even the latest OpenWRT is vulnerable to this, I'm running OpenWRT 25.12.6 and the kernel version is 6.12.112

      • snek_case 50 minutes ago

        IIUC it doesn't have any listening sockets open on WAN by default at least?

geye1234 4 hours ago

My home firewall runs Ubuntu. It doesn't accept (new) incoming packets from the internet. I don't have any IoT devices except printers, whose packets the firewall rejects, and has done since I bought them. Do I need to do anything apart from wait for the patch to become available?

  • nikanj 1 hour ago

    How does your internet work, if the firewall doesn't accept incoming packets?

hansvm 52 minutes ago

I was sorely tempted to fully bypass the kernel for networking before, and this isn't exactly giving me warm fuzzies for staying.

lakeviewterrace 5 hours ago

Is OpenWRT affected? Because that would be a real fawkin problem.

  • lunar_rover 5 hours ago

    OpenWrt doesn't open ports by default so I think the impact is minimal, unless this can breach nftables as well. CGNAT also mitigates this as a side effect.

    If you have services open on the IPv4 net however, close them immediately as a precaution.

    • basilikum 4 hours ago

      How do you plan on reopening them again after you've closed 443 and 22?

      • pamcake 1 hour ago

        Admin interfaces should never have been exposed publicly in the first place (and aren't by default). Remote admin over wireguard or sth if you must.

bana-io 5 hours ago

Without a test-case, read POC, how do I verify if my server is affected?

theteapot 5 hours ago

What is a "multipath TCP listener"?

  • dist-epoch 5 hours ago

    You have a Wifi network interface and a wired Ethernet one, multipath is somehow combining the two together.

    • sweetjuly 5 hours ago

      In addition to aggregating, it can also be useful in cases where one link is much slower or higher latency. For example, if you're sitting in your driveway trying to get directions in maps while your phone is still on your very weak wifi network, it's a better user experience to have it to attempt the request using both radios concurrently so that it can fallback to cellular without waiting for a timeout/connection error if you're too far for wifi to actually work well.

      • cowlevel 4 hours ago

        Do apps actually use this possibility though?

  • Noxwizard 5 hours ago

    I had to look it up too since I hadn't heard of it. It's an extension to TCP that allows responses across different NICs. Sort of like Link Aggregation on to a switch, except it can go out dissimilar interfaces, like your wifi connection and your hardwired connection. Looks like you have to opt into it when you set up your socket: https://docs.kernel.org/networking/mptcp.html

  • wahern 5 hours ago

    See https://en.wikipedia.org/wiki/Multipath_TCP

    It's an extension to TCP that, similar to QUIC, allows you to use multiple address/port pairs to transmit data over a single logical stream. Both client/initiator and server/listener have to opt into the extension. This might need to be enabled explicitly by the application[1], which Go apparently does for you, or judging from other posts may be enabled by default systemwide, depending on your platform.

    AFAIU, a major user of MPTCP is Apple and the iPhone, and the ubiquity of iPhone clients motivated implementation in and deployment on Linux servers.

    [1] https://docs.kernel.org/networking/mptcp.html#sockets-api

  • jacquesm 5 hours ago

    A listener is a piece of software that advertises itself as available to inbound connections. You can do this on a variety of protocols.

    Multipath TCP is a neat trick that allows a single TCP connection (TCP = Transport Control Protocol, a stateless protocol for long running connections) to use multiple physical interfaces. You could do something similar before MTCP using bonding, but this was annoying to set up and usually required application level code to efficiently use the bonded connection. MTCP makes this much simpler from an application level point of view and it can use widely diverse underlying transport layers at the same time (for instance, WiFi, Cellular and wired connections).

    • ButlerianJihad 28 minutes ago

      > Transport Control Protocol, a stateless protocol

      TCP is stateful by definition, and that is why it supports robust error correction and reliable streams of data. UDP is its stateless counterpart.

      > bonding, ... usually required application level code

      No, it doesn't. https://en.wikipedia.org/wiki/Link_aggregation

      > underlying transport layers

      TCP is in the transport layer! The layers which you name are lower, such as Layer 2 (Data Link)!

      MTCP, being in the transport layer, is working at a higher level of abstraction than bonding or link aggregation. There is no need for application-layer support, but it is possible, and easier, with MTCP than with the Layer 2 solutions, because MTCP is in the transport layer. That is why Go was able to activate it, and the POC uses it, because MTCP controls can be exposed at that level.

kaoD 1 hour ago

What does this enable an attacker to do exactly? RCE? DoS? Unknown?

lakeviewterrace 4 hours ago

The linked source spun up my fans with 100% GPU utilization. Is there some... unwelcome... script running?

frunzales 2 hours ago

If you run a custom kernel chances are you're not affected:

# CONFIG_MPTCP is not set

0xbadcafebee 2 hours ago

The most terrifying part of this is all the devices that might be affected. Ignore servers and desktops. Linux 4.4 came out nearly 11 years ago. While most Linux devices' firmware is actually more ancient than that (Linux 2.x and 3.x isn't uncommon), any device that did ship with Linux 4.4+ is going to get hacked, because nobody patches those devices. Any smart device in the world that isn't a server, desktop, or microcontroller, is probably running Linux.

As part of the Software Building Code (that we don't have, and desperately need), one of the things we should have is mitigation for these abandoned internet safety risks. Here's how I would define that section:

  Section 4    Connections to Public Internet
  Section 4.1  Device Support
    Devices connected to the public internet WILL require one of the following:
      a) Guaranteed LTS support for a minimum of 10 years
      b) Guaranteed rolling release support for a minimum of 10 years
    Devices without this support are not permitted to be connected to the public internet.
  Section 4.2  Vendor Responsibility
    When releasing devices, vendors must determine whether this device is certified for
    public internet use. Support must be maintained according to S4.1. Failure to comply will
    result in fines of up to $5,000 per affected device.
  Section 4.3  Installer Responsibility
    Any device connected to the public internet which is not certified for public internet
    use is in violation, and will be subject to fines of up to $500 per affected device.
  Section 4.4  Device Owner Responsibility
    Any installed devices will be replaced once they reach their End Of Life period,
    or after 10 years, whichever comes first. Installed devices in use that exceed this
    period are in violation, and subject to fines of up to $250 per affected device.

(These fines are tiny compared to the fines for things like fire code violations, but enough money that a company, contractor, or individual would rather fix their device than pay the fines)

jeffbee 1 hour ago

There are microkernel operating systems out there that run the network stack in isolated, unprivileged contexts. Some of them are even not written in C.

api 5 hours ago

2027 is going to be the year of two to three major CVEs per day.

The discourse on this is weird, sounds at times as if these are “because of AI.” These are mostly pre-existing bugs, some very old, and they’ve been lurking. If they all get found we exit the other side more secure and reliable.

  • jstanley 4 hours ago

    > If they all get found we exit the other side more secure and reliable.

    I agree, but as yet we have no idea how much pain we have to pass through to get to the other side.

  • wry_xy 3 hours ago

    I went on a security kick early this year, locking down everything as much as I could. Build your systems with the assumption that you WILL get hacked. Limit blast radius. Be prepared.

    The next few years will be crazy, but you're right, we'll come out the other side more secure than ever before. Just gotta make it that far!

    • jijijijij 2 hours ago

      Will be interesting to see, if AI will cause an increased demand for sysadmins. Not sure companies will go "Make no mistakes" on their (production) infrastructure.

  • Gigachad 3 hours ago

    On the other side we have a Linux networking stack written in Rust.

oger 6 hours ago

MikroTik routers seem affected but mitigations are available.

Watch your Linux systems for kernel updates. Reboot!

  • tgv 5 hours ago

    If you use sysctl to disable mptcp, you need to do that again after each reboot.

jmclnx 5 hours ago

If I am reading this right, Slackware 15.0 is already fixed:

     % uname -a
     Linux XXXX 5.15.223 #1 SMP PREEMPT Thu Oct 22 00:03:07 CDT 2026
     x86_64 Intel(R) Core(TM) i7-4810MQ CPU @ 2.80GHz GenuineIntel GNU/Linux
  • cyberpunk 4 hours ago

    You’re still on slackware? I’ve not thought about it in years! How’re things over there?

    • tosti 3 hours ago

      It works mostly fine, pretty easy to work with, might perform well when you're sleeping / not around, packages are old (not neccesarily a bad thing). The default kernel is vintage 5.15, so just compile your own. Also elilo really sucks so bring your own bootloader while you're at it.

jonathanstrange 3 hours ago

I tried to find a mitigation using a ufw filter that rejects IPv4 packets with too large headers but it didn't work. It broke something essential and I had to switch it off again. I'd be interested in hearing about a temporary mitigation using firewall rules.

  • superkuh 45 minutes ago

    Add the below rule onto your machine's /etc/ufw/before.rules to mitigate it.

        # CVE-2026-98432 mitigation: drop TCP packets carrying IPv4 extended options
        -A ufw-before-input -p tcp -m u32 --u32 "0>>24&0xF=6:15" -j DROP
    

    Any value >5 in this field means ip extended header options and so values of 6 through 15 should be dropped. Note that I don't just drop syn packets like the mptcp exploit because any tcp packet could do it in theory.

    This works for me on multiple servers and home desktops and my hardware linux firewall/router. I did it a couple days ago when this was first announced. The iptables counter for matches haven't gone up at all on my VPS servers that gets lots of traffic. The counter only goes up when I manually trigger it to test. Everything continues to work nominally with these in place.

dofm 4 hours ago

[06:00]

ogogmad 5 hours ago

How are people finding Fil-C? It's designed to avoid things like this.

  • cowlevel 4 hours ago

    Does it support writing kernels?

  • _flux 4 hours ago

    It might be bit of an effort to get Fil-C compiling the Linux kernel. As I understand it, it would amount to running garbage collector in the kernel, so some care would probably need to be taken to ensure it doesn't stop things at the wrong time, e.g. interrupts.

TacticalCoder 2 hours ago

Let me guess... The bug is in C code?

(reading TFA)

    net/ipv4/af_inet.c
    net/ipv4/tcp_ipv4.c

Ah yup.

And moreover it's a security issue found by LLMs.

It's kinda a really bad time to be a C-loving, AI-hating, fanboi.

Do we at least entertain the idea that some rewrites of some things in safer languages could be a desirable goal? (not saying it's practical or not: just asking if C lovers are willing to reflect a bit on what's going on atm).

  • TZubiri 2 hours ago

    maybe

    i’d focus on writing new stuff with rust though, not rewriting old stuff

    and time will tell whether it actually reduces bugs or just change the failure modes to something else

    also C will always be there in some way or the other, at least in conventions and syntax

grommz 3 hours ago

Who wrote the bug? Very likely someone at Redhat.

jck86 3 hours ago

Finally a usecase for mptcp on linux. Been waiting and trying off and on for years to get it to do something, but now it can give a nice remote root shell. Well, not to me, I just get to patch devices.

rurban 4 hours ago

In an earlier report, it said only affected is kernel 4.4, not all since. This quite dramatic now.

I see. https://nvd.nist.gov/vuln/detail/cve-2026-98432 affected versions format is the culprit. Entirely unusable. We do have versions, branch names and tags for a reason.

  • pizza234 4 hours ago

    Wrong. Every kernel from 4.4 onward is affected until the fixed releases (5.10.272, 5.15.223, 6.1.190 and so on).

    • Mawr 2 hours ago

      Right. The "Affected Products" section on https://nvd.nist.gov is absolutely useless and highly misleading. I don't understand how this can be the case for something so security critical.