The Linux kernel's crypto: algif_skcipher module had a vulnerability where the asynchronous I/O (AIO) path in skcipher_recvmsg() passed a socket-wide IV pointer directly into the cryptographic request. After submitting the request asynchronously, the socket lock was released, allowing a concurrent sendmsg(ALG_SET_IV) call to overwrite the IV. For CTR and stream cipher modes, this caused IV/keystream reuse, which can leak plaintext to unprivileged users. Attempts to snapshot the IV per request failed due to the way IV chaining and writeback were handled, especially for ciphers with zero state size like CBC and CTR. The fix was to disable asynchronous processing for this code path, making io_submit() complete synchronously, thus removing the race conditions. This fix aligns with an upstream commit that removed AIO socket support entirely but is scoped narrowly to avoid invasive changes in stable kernels. Testing showed the fix eliminated attacker IV injection and preserved correct cryptographic output.

An unprivileged local user could exploit this vulnerability to recover plaintext from concurrent cryptographic operations by causing IV reuse in CTR/stream cipher modes. This compromises the confidentiality of data processed by the affected kernel crypto subsystem. The vulnerability affects cryptographic operations using AF_ALG sockets with asynchronous I/O in the algif_skcipher module.

A fix is available and has been applied by disabling asynchronous processing in the affected crypto code path, forcing synchronous operation to prevent IV races. Users should update to a Linux kernel version that includes this fix. Since this is a kernel-level fix, applying the official kernel update is the recommended remediation. No additional mitigations are indicated or necessary.