Bug 2403545 (CVE-2025-39964)

Summary: CVE-2025-39964 kernel: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A race condition was found in the Linux kernel cryptographic user API, AF_ALG in the way concurrent writes to the same AF_ALG socket are handled. Interleaved data and inconsistent internal socket state may result. A local user could use this flaw to crash the system or corrupt cryptographic operation results, causing a denial of service or data integrity issues.
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Description OSIDB Bzimport 2025-10-13 14:01:33 UTC 
In the Linux kernel, the following vulnerability has been resolved:

crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Issuing two writes to the same af_alg socket is bogus as the
data will be interleaved in an unpredictable fashion.  Furthermore,
concurrent writes may create inconsistencies in the internal
socket state.

Disallow this by adding a new ctx->write field that indiciates
exclusive ownership for writing.
Comment 1 Jon Moroney 2025-10-13 16:01:31 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025101334-CVE-2025-39964-7964@gregkh/T