REDHAT-BUG-2481882: Low severity OpenSSL OpenSSL vulnerability

PKCS#12 Files with PBMAC1 Are Accepted with Short HMAC Keys

PKCS#12 Files with PBMAC1 Are Accepted with Short HMAC Keys (CVE-2026-34181) Severity: Low

Issue Summary: The PKCS#12 file processing fails to perform sufficient input validation for files that use Password-Based Message Authentication Code 1 (PBMAC1) integrity mechanism allowing a certificate and private key forgery.

Impact Summary: An attacker impersonating a user can cause a service reading PKCS#12 files to accept forged certificates and private keys with a 1 in 256 probability.

If a service accepting PKCS#12 files is using passwords for authenticating the received files, the attacker can create unencrypted PKCS#12 files that use PBMAC1 authentication that specifies an HMAC key of only one byte, allowing them to craft a file that will be accepted with a 1 in 256 probability. That would then cause the service to accept a certificate and private key controlled by the attacker.

The FIPS modules are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

OpenSSL 4.0, 3.6, 3.5, and 3.4 are vulnerable to this issue.

OpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue as they do not support PBMAC1 in PKCS#12.

OpenSSL 4.0 users should upgrade to OpenSSL 4.0.1. OpenSSL 3.6 users should upgrade to OpenSSL 3.6.3. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.7. OpenSSL 3.4 users should upgrade to OpenSSL 3.4.6.

This issue was reported on 2nd March 2026 by Pavol Žáčik (Red Hat). This issue was also reported on 16th April 2026 by Alex Gaynor (Anthropic).

The fix has been developed by Alicja Kario (Red Hat).