Out-of-Bounds Stack Write vulnerability in the blst_sha256_bcopy assembly routine of the blst cryptographic library. The flaw is caused by a missing zero-length guard in the copy loop implementation. When blst_keygen_v5() (or related key generation functions) is called with a valid non-NULL salt pointer and salt_len equal to zero, the length counter underflows, causing the loop to execute and write beyond intended stack boundaries. This results in memory corruption and immediate process termination. This issue can be triggered without authentication or user interaction if an application exposes key generation with attacker-controlled salt parameters, leading to a denial-of-service condition.