As mentioned earlier in this thread, the su corruption route was only one possible strategy to be used by this exploit.

Here's another variant of the exploit that doesn't have to rely on such things to achieve its goal.

For example, the simple escalate argument simply removes the password requirement for su'ing to root. There are other payloads also possible.

Such exploits will not have process 'su' launched '/bin/sh IOCs in the syslogs. Perhaps all that is relevant is the alg: No test for authencesn(hmac(sha256),cbc(aes)) (authencesn(hmac-sha256-lib,cbc-aes-aesni)) part. But there's no evidence of what was done.

Unlike what the buffoons at Theori published as a "mitigation", the folks at Red Hat actually published a viable mitigation for CopyFail CVE-2026-31431.

Specifically, edit your grub (or whatever you use to load your kernel) configuration to have one of the following arguments:
initcall_blacklist=algif_aead_init
initcall_blacklist=af_alg_init
initcall_blacklist=crypto_authenc_esn_module_init

With such boot arguments to the Linux kernel, the affected bits won't be reachable.

What went wrong with this case?

Theori appear to have only contacted the linux kernel devs with the vulnerability, as opposed to going the usual CVD route that includes all of the major Linux distros.

Why is this a problem? Since the linux kernel became a CNA, there has been a flood of CVEs for the Linux kernel. The Linux kernel devs' arguments is that any given kernel flaw could presumably be leveraged to behave as a vulnerability, and it's not worth their time to determine "vulnerability" or "not a vulnerability". Everything gets a CVE.

Now the case with copy.fail? It was indeed reported to the kernel devs. And it got a CVE. A single CVE buried in flood of all of the Linux kernel CVEs.

And it appears that every distro on the planet was blindsided by this proven-exploitable vulnerability because they were not given any warning. Or even any suggestion to pick this single CVE out of the sea of Linux kernel CVEs as worth cherry picking.

Much to the chagrin of the Linux devs, RHEL doesn't use up-to-date Linux kernels. They cherry pick CVEs to backport to their chosen kernel version. (e.g. the latest and greates RHEL 10.1 uses 6.12.0, which was released November 17 2024). And in this world where bad actors like Theori don't involve vendors in vulnerability coordination, and just about every Linux kernel bug gets a CVE, this workflow fails. Hard.

Good times...

While this vulnerability seems to be discovered using AI ("Xint Code"), I have to assume that they also let the AI decide how to do the vulnerability coordination as well.

• major builds are out as of this writing 😂
  
  No distros have official updates for CVE-2026-31431. Fedora 42 and newer have updates, but no official advisory or acknowledgement of CVE-2026-31431. So with them it's unclear if it's even intentional. Red Hat, Ubuntu, Amazon Linux, and Suse all have advisories as of now, but NO updates.

• disable the algif_aead module as a mitigation. 😂
  
  Bespoke distros like RHEL don't use a module, it's compiled into the kernel.

I can't figure out what the Xint Code angle is with this copyfail stuff. On one hand, yes, it is a true vulnerability that affects a LOT of Linux distros available. And they did submit the bug for fixing to the upstream kernel people.

BUT the CVE has only existed for a week. And NONE of the distros IN THEIR ADVISORY had updates available at the time that they pulled the trigger for publication of the shiny copy.fail website.

I struggle to think of how this even happens. In all my years of infosec, you're either on board with doing CVD (e.g. coordinating with the former CERT/CC) or you're not (dropping 0day). But this all fits bizarrely in the middle. The publication gives the guise that they did the right thing, (and please use our AI services). But at the same time, they clearly chose to release the vulnerability details and functional exploit before any distro had the ability to properly do anything about it.

Either these Xint Code (Theori) people have a hidden agenda or ulterior motive that we aren't aware of yet. Or they're just really bad at coordinated vulnerability disclosure. You pick.