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

Severity: high (CVSS 7.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-09 · updated 2026-07-23
Weakness: CWE-354

Description

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.

Affected products

OpenSSL: from 3.4.0 before 3.4.6; from 3.5.0 before 3.5.7; from 3.6.0 before 3.6.3; 4.0.0 — fixed in 3.4.6, 3.5.7, 3.6.3

How to fix

Upgrade to a fixed version: OpenSSL 3.4.6, 3.5.7, 3.6.3. Check the vendor advisory for mitigations.

References

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