- 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.
That doesn't track. Apple iPhones are a major user of MPTCP and they report the majority of requests supporting MPTCP, IIRC 70+%.
> 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...
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.
LTS doesn't work if you want immediate fixes like the current environment requires.
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.
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".
https://ubuntu.com/project/docs/SRU/reference/sru-verificati...
or download the individual package (and dpkg --install ... but this doesn't check signatures)
https://ubuntu.pkgs.org/26.04/ubuntu-proposed-main-amd64/lin...
RHEL runs with MP-TCP disabled by default, they initially listed it as Important only to later raise it to Critical.
IMNSHO this makes them unfit for purpose. I think this is the nail in the coffin for Ubuntu for me.
https://forum.proxmox.com/threads/cve-2026-98432-in-proxmox-...
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...
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?
"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."
The listed kernels are in the "proposed" component (and not yet in "security" or "udpates") if you want to pull them down onto canary systems for testing before going to production.
> 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-...
It would be great if they introduced mitigations for this vulnerability though.
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.
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...
An entire ecosystem of malware crawling and cohabiting in them.
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).
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.
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.
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.
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.
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
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.
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.
no idea, but at least Tailscale and Caddy were opening MPTCP sockets on servers I checked.
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.
I was talking about the Anthropic blog post, only Go/Caddy enable multipath TCP listeners by default.
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.
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.
https://www.reddit.com/r/openwrt/comments/1xka85h/is_the_ope...
They say 25.12-SNAPSHOT has it fixed
If you have services open on the IPv4 net however, close them immediately as a precaution.
actual link: https://nvd.nist.gov/vuln/detail/cve-2026-98432
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).
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
# CONFIG_MPTCP is not set
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.
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!
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.
Watch your Linux systems for kernel updates. Reboot!
% 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(reading TFA)
net/ipv4/af_inet.c
net/ipv4/tcp_ipv4.c
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).
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.
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.