OpenSSL Use After Free Vulnerability - CVE-2026-45447

Issue summary: A specially crafted PKCS7 or S/MIME signed message could trigger a use-after-free during PKCS7 signature verification. Impact summary: A use-after-free may result in process crashes heap corruption or potentially remote code execution. When processing a PKCS7 or S/MIME signed message if the SignedData digestAlgorithms field is present as an empty ASN.1 SET OpenSSL may incorrectly free a caller-owned BIO during PKCS7_verify(). A subsequent use of the BIO by the calling application results in a use-after-free condition. In the common case this occurs when the application later calls BIO_free() on the BIO originally passed to PKCS7_verify(). Depending on allocator behavior and application-specific BIO usage patterns this may result in a crash or other memory corruption. In some application contexts this may potentially be exploitable for remote code execution. Applications that process PKCS7 or S/MIME signed messages using OpenSSL PKCS7 APIs may be affected. Applications using the CMS APIs for this processing are not affected. The FIPS modules in 4.0 3.6 3.5 3.4 and 3.0 are not affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.