CVE-2025-39931: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel's crypto subsystem was discovered and disclosed on October 4, 2025. The issue affects the af_alg (Algorithm Framework) component, specifically in the af_alg_sendmsg function where ctx->merge may contain a garbage value from a previous loop if an error occurs (NVD, Ubuntu).

The vulnerability occurs in the af_alg_sendmsg function of the Linux kernel's crypto subsystem. When an error causes af_alg_sendmsg to abort, the ctx->merge variable may retain a garbage value from the previous loop iteration. This retained garbage value can trigger a crash during subsequent calls to af_alg_sendmsg when it attempts to perform a merge operation that isn't possible (NVD).

The primary impact of this vulnerability is system stability, as it can lead to kernel crashes when the affected code path is triggered. This occurs when the af_alg_sendmsg function attempts to perform invalid merge operations with garbage values (NVD).

The fix involves setting ctx->merge to zero near the start of the loop in af_alg_sendmsg, preventing the retention of garbage values that could cause crashes. This patch has been implemented in the Linux kernel (NVD).