A race condition exists in the Linux kernel’s AF_ALG socket path when an asynchronous skcipher operation is executed. A concurrent sendmsg(ALG_SET_IV) can overwrite the socket‑wide IV while the request runs, causing the in‑flight request to use an attacker‑controlled IV. This IV reuse in CTR or stream ciphers enables an unprivileged user to recover the plaintext of a concurrent encryption operation.

All Linux kernel releases that expose the AF_ALG asynchronous path before the fix, such as versions prior to the commit that removed the AIO branch from crypto/algif_skcipher.c (e.g., kernel 6.6 and earlier). The patch forces synchronous processing, eliminating the race for these affected kernels.

The flaw is local and requires an attacker to execute both a cryptographic request and an ALG_SET_IV ioctl on the same AF_ALG socket. Although EPSS is unavailable and the vulnerability is not listed in CISA’s KEV catalog, the potential to recover plaintext makes the impact high. The CVSS score is not supplied, but the flaw represents a critical cryptographic weakness that can be exploited by any user with access to AF_ALG sockets.