Executive Summary
According to a report from Xint published on 29 April 2026, a Linux kernel vulnerability named “Copy Fail” has affected multiple major Linux distributions released since 2017. The flaw, designated CVE-2026-31431, allows a local, unprivileged user to escalate privileges to root by exploiting improper handling of data copying within the kernel. The vulnerability enables potential threat actors to perform controlled writes to the page cache, allowing modification of critical binaries in memory without altering files on disk. This technique significantly reduces detection likelihood, as standard file integrity and monitoring tools may not identify any evidence of tampering. The vulnerability presents a broad risk due to its reliability and applicability across multiple Linux environments. A patch, commit a664bf3, has been released to address CVE-2026-31431.
Key Takeaways
- The vulnerability originates within the Linux kernel’s cryptographic (AF_ALG) subsystem, specifically involving interactions between user space and kernel memory.
- The exploit is caused by improper handling of data copying within the Linux kernel.
- The “Copy Fail” vulnerability allows local privilege escalation to root on affected Linux systems.
- The vulnerability enables controlled modification of the page cache, allowing changes to binaries in memory.
- No modifications are made to files on disk, which may limit visibility through traditional file integrity monitoring.
- The issue affects multiple major Linux distributions released since approximately 2017.
- Xint researchers validated the exploit across several Linux distributions, including Ubuntu 24.04 LTS, Amazon Linux 2023, RHEL 10.1, and SUSE 16.
Mitigation Options
The Xint research team has provided mitigations, which can be found below:
- Patch the kernel: The fix reverts AF_ALG AEAD to out-of-place operation, eliminating page cache pages from the writable scatterlist.
- Update your distribution’s kernel package: Major distributions should ship the fix through normal kernel package updates.
- For immediate mitigation: Block the AF_ALG socket creation via seccomp or blacklist the algif_aead module.
