A logical vulnerability in the cryptographic subsystem of the Linux kernel allows unprivileged local users to elevate their rights to the root level. Identificada as CVE-2026-31431 and nicknamed Copy Fail, the flaw affects distributions released since 2017. Desenvolvedoras of the main distributions have already distributed patches to correct the problem. The exploit works through an Python script with just ten lines and 732 bytes.
Mecanismo technical vulnerability Copy Fail
The bug resides in the authenticationsn template, a component used in authenticated encryption operations. The flaw allows local users to write four controlled bytes to the page cache of any readable file. Essa change directly affects kernel loading of binaries, creating a gateway for privilege escalation.
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The problem originated from a change implemented in 2017 in the algif_aead module. Essa change allowed page cache pages to be available for writing in certain scatterlist scenarios. Diferentemente Unlike other classic vulnerabilities, Copy Fail does not require race conditions to function, significantly simplifying its exploitation.
Pesquisadores of Theori identified the issue with the support of artificial intelligence-based scanning tools. The exploit alters the binary in memory without triggering file system event-based detection mechanisms such as inotify. Isso makes detection more complex in real time.
Impacto in production and containerization environments
- CVE-2026-31431 received a score of 7.8 out of 10, classified as high severity.
- Exploração works in multi-tenant environments and containers with a shared kernel.
- Page shared cache on the host allows potential escape of Kubernetes containers.
- Não is remotely exploitable in isolation, but amplifies other attack vectors.
Sistemas that run untrusted code, such as CI/CD runners or shared servers, are more at risk. Host-level shared page cache poses a concrete escape threat in containerized environments. Administradores that manage multiple tenants or third-party workloads should prioritize immediate kernel upgrade.
Distribuições now offers corrected patches
Debian, Ubuntu and SUSE have already made updated kernels available with the fix. Red Hat has changed its initial deferral position and now offers the patch in sync with the ecosystem. Fedora has also committed the fix to its repositories. Patch rollout occurs in a coordinated manner between the main maintainers, with Debian and Ubuntu publishing new kernels with the necessary revert to the in-place behavior of algif_aead.
The Linux community follows the process on discussion lists and technical forums. Muitos administrators have already started the application on critical servers. Coordination between vendors limited the period of exposure after responsible disclosure of the failure.
Temporary Mitigation Medidas
A temporary measure is to disable the algif_aead module, preventing the vulnerable component from loading in most scenarios. Administradores can create the file /etc/modprobe.d/disable-algif.conf with the content install algif_aead /bin/false. Após this, you must execute rmmod algif_aead to remove the module if it is loaded.
Essa configuration may affect applications that explicitly depend on the encryption module. Testes in staging environments are recommended before application in production. Official Atualizações remain the definitive and most secure solution to completely resolve the vulnerability.
Contexto Discovery and Future Prospects
Copy Fail resembles historical faults such as Dirty Cow and Dirty Pipe, but stands out for its simplicity of exploration and breadth of scope. The recent increase in vulnerability reports is directly related to the use of artificial intelligence tools in bug hunting. Pesquisadores estimate that the majority of installations active since 2017 require immediate attention to maintain operational safety.