OpenSSL: use-after-free in PKCS7_verify when a signed message carries an empty digestAlgorithms set

Impact

If a PKCS#7 or S/MIME SignedData message presents digestAlgorithms as an empty ASN.1 SET, PKCS7_verify() frees a BIO that the caller still owns. The application's later use of that BIO - most commonly its own BIO_free() - is then a use-after-free, giving crashes, heap corruption, or in some application shapes potentially remote code execution. This hits verification code paths rather than serving paths, so on a fleet the exposure is in whatever checks signatures on artifacts, packages or tokens. Applications using the CMS APIs for the same job are not affected, and the FIPS modules in 4.0, 3.6, 3.5, 3.4 and 3.0 are outside the affected code.

Who can reach it

An attacker who can hand a crafted signed message to a service that verifies it with the OpenSSL PKCS#7 APIs. The CVSS vector assumes low privileges - typically an authenticated user able to submit content for verification.

What to do

Take the fixed OpenSSL from your distribution (Red Hat is issuing it across RHEL 7 ELS, 8 with its EUS/TUS/SAP streams, and 10). As with any libcrypto update, the fix only takes effect once each linked daemon is restarted - patch, then restart the verifying services, or reboot the node. The record gives commits rather than a fixed version string; do not assume a number that is not in the advisory.

References

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