This vulnerability is an out-of-bounds read in the AES-CFB128 implementation on x86-64 systems that enable AVX‑512 and VAES. The over‑read can access up to fifteen bytes beyond the supplied input buffer when the function processes a partial block that spans a page boundary. Because the read is performed only for addresses that are not really part of the buffer, it may trigger a fault if the next page is unmapped. The fault manifests as a process crash, resulting in a denial of service. No sensitive data is disclosed because the victim does not record the read bytes.

Affects OpenSSL versions that use the AVX‑512 accelerated AES‑CFB128 path on x86‑64 hosts. This includes the OpenSSL FIPS module version 3.6. No other architectures or non‑AVX‑512‑enabled x86‑64 systems are impacted. The issue does not exist in TLS/DTLS protocols, which use separate cipher suites. The vulnerability only materializes when an application has an unfinished block from a previous call and the next call provides fewer bytes than required to finish it, and the input buffer ends precisely on a page boundary with the succeeding page unmapped.

The bug is rated CVSS 9.1, indicating high impact, yet the exploit probability is extremely low. EPSS suggests less than 1% chance of exploitation, and the vendor did not list it in KEV. In order to trigger the crash, an attacker would need to craft ciphertext that forces the decryption routine to read outside buffer bounds, a scenario that also depends on the memory layout of the victim process. Because typical applications avoid placing data on page boundaries, and because CFB mode is not used in the most common TLS implementations, the practical risk to most deployments is modest, leading the vendor to classify it as low severity.