A logical flaw in the cryptographic subsystem of the Linux kernel allows unprivileged local users to elevate their rights to the root level. Desenvolvedores major distributions have already started distributing patches to fix CVE-2026-31431, known as Copy Fail.
The problem is in the authenticationsn template, used in authenticated encryption operations. Ele makes it possible to write four controlled bytes to the page cache of any readable file. Essa change directly affects kernel loading of binaries.
Detalhes authentication failure technicians
The bug arose 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. Diferente From other classic vulnerabilities, Copy Fail does not require race conditions to work.
Pesquisadores of Theori identified the issue with the support of AI-based scanning tools. The proof of concept is an Python script with just 10 lines and 732 bytes. Ele modifies setuid binaries and runs code with elevated privileges on most distributions released since 2017.
- CVE-2026-31431 received a score of 7.8/10, classified as high severity
- Exploração works in multi-tenant environments and containers with shared kernel
- Page shared cache on host allows potential escape of Kubernetes containers
- Não is remotely exploitable in isolation, but amplifies other vectors
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.
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Impacto in production and container environments
Sistemas that run untrusted code, such as CI/CD runners or shared servers, are more exposed. Shared page cache at the host level poses a concrete escape risk in containerized environments.
Distribuições like Debian, Ubuntu and SUSE have already made updated kernels available. Red Hat has changed its initial deferral position and is now offering the patch in sync with the ecosystem. Outros vendors, including Fedora, have also confirmed the fix.
Administradores that manage multiple tenants or third-party workloads should prioritize the upgrade. The bug gained rapid visibility after coordinated disclosure.
Como mitigate until full patch applied
A temporary measure is to disable the algif_aead module. Isso prevents the vulnerable component from loading in most scenarios.
- Crie the file /etc/modprobe.d/disable-algif.conf with the content: install algif_aead /bin/false
- 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 solution.
Atualizações released by distributions
Patch rollout occurs in a coordinated manner between the main maintainers. Debian and Ubuntu have published new kernels with the required revert to the in-place behavior of algif_aead. SUSE followed suit with updated packages.
Red Hat has aligned its guidance after internal review. The Linux community follows the process on discussion lists and technical forums. Muitos administrators have already started the application on critical servers.
The recent increase in vulnerability reports is directly related to the use of AI tools in bug hunting. Programas like Internet Bug Bounty recorded a high volume of submissions, which led to temporary adjustments to the award processes.
What changes for Linux sysadmins
The discovery reinforces the need to keep kernels up to date, especially on shared infrastructures. Security Equipes now more closely evaluates cryptographic modules and kernel components loaded by default.
Copy Fail resembles historical faults such as Dirty Cow and Dirty Pipe, but stands out for its simplicity of exploration and breadth of scope. Public PoC facilitates testing, but also accelerates potential abuse in unpatched environments.
Pesquisadores estimate that most installations active since 2017 require immediate attention. Coordination between vendors limited the exposure period after responsible disclosure.