A vulnerability in OpenSSL versions from 0.9.0 up to but not including 0.10.78 allows an out-of-bounds read when a PEM password callback returns a length larger than the buffer size. This occurs because the length returned by the user's password callback is not validated against the buffer size, leading to reading past the buffer end during key derivation. OpenSSL 3.x is not affected. The issue is fixed in version 0.10.78, which treats oversized lengths as callback failures.