OpenSSL PKCS#12 PBMAC1 short HMAC key acceptance allows certificate and private key forgery
CVE-2026-34181 is a low-severity input validation flaw in OpenSSL PKCS#12 file processing. When processing PKCS#12 files that use the Password-Based Message Authentication Code 1 (PBMAC1) integrity mechanism, OpenSSL fails to sufficiently validate the PBMAC1 parameters and accepts files specifying an HMAC key of only one byte. As a result, an attacker can craft an unencrypted PKCS#12 file authenticated with PBMAC1 such that integrity verification succeeds with a 1 in 256 probability, causing the receiving service to accept attacker-controlled certificate and private key material as valid. According to the provided advisory context, affected versions are OpenSSL 4.0.0 before 4.0.1, 3.6.0 before 3.6.3, 3.5.0 before 3.5.7, and 3.4.0 before 3.4.6. The vulnerable code is outside the OpenSSL FIPS module boundary, so FIPS modules are not affected.
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Recent activity
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An OpenSSL vulnerability addressed in Alpine Linux 3.24.1 as part of the June 9, 2026 advisory.
A low-severity OpenSSL PKCS#12 input validation flaw where PBMAC1 files with very short HMAC keys may be accepted, enabling certificate and private key forgery with limited probability.
The version that knows your environment.
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Every observed campaign linking this CVE to a named adversary.
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YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.