Patches land for authencesn flaw enabling local privilege escalation
Developers of major Linux distributions have begun shipping patches to address a local privilege escalation (LPE) vulnerability arising from a logic flaw.
The newly disclosed LPE, dubbed Copy Fail (CVE-2026-31431), comes from a vulnerability in the Linux kernel's authencesn cryptographic template.
"An unprivileged local user can write four controlled bytes into the page cache of any readable file on a Linux system, and use that to gain root," the writeup from security biz Theori explains.
The kernel reads the page cache when it loads a binary, so modifying the cached copy amounts to altering the binary for the purpose of program execution. But doing so doesn't trigger any defenses focused on file system events like inotify.
The proof of concept exploit is a 10-line, 732-byte Python script capable of editing a setuid binary to gain root on almost all Linux distributions released since 2017.
Copy Fail is similar to other LPE bugs such as Dirty Cow and Dirty Pipe, but its finders claim it doesn't require winning a race condition and it's more broadly applicable.
It's not remotely exploitable on its own – hence LPE – but if chained with a web RCE, malicious CI runner, or SSH compromise, it could be relevant to an external attacker. The bug is of most immediate concern to those using multi-tenant Linux systems, shared-kernel containers, or CI runners that execute untrusted code.
According to Theori, the vulnerability also represents a potential container escape primitive that could affect Kubernetes nodes, because the page cache is shared across the host.
Linux distros Debian, Ubuntu, and SUSE have issued patches for the problem, as have overseers of other distros.
Red Hat initially said it was going to defer the fix but later changed its guidance to indicate it will go along with other distros and patch promptly.
The CVE has been rated High severity, 7.8 out of 10.
Theori researcher Taeyang Lee identified the vulnerability, with the help of the company's AI security scanning software, Xint Code.
The number of bug reports has surged in recent months, helped by AI-powered flaw-finders. Microsoft just reported the second largest number of patches ever.
Dustin Childs, head of threat awareness for Trend Micro's Zero Day Initiative, expects this is due to security teams using AI to hunt bugs. "There are many things we could speculate on to justify the size, but if Microsoft is like the other programs out there (including ours), they are likely seeing a rise in submissions found by AI tools," he wrote earlier this month.
AI-assisted vulnerability research recently prompted the Internet Bug Bounty (IBB) program to suspend awards until it can understand how to manage the growing volume of reports. ®