CVE-2026-34181: PKCS#12 Files with PBMAC1 Are Accepted with Short HMAC Keys
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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.4.6 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.5.7 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.6.3 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 4.0.1 - Configuration
Avoid accepting PKCS#12 files using PBMAC1 authentication (PBMAC1 with an HMAC key of only one byte). Configure the service/application to not use or accept PBMAC1 for PKCS#12 password authentication, if this option is available in your deployment.
OpenSSL PKCS#12 (PBMAC1) PBMAC1 support in PKCS#12 processing = disable - Compensating control
If you use OpenSSL 4.0, 3.6, 3.5, or 3.4, restrict any service that accepts PKCS#12 files to sources you trust, to reduce the chance an attacker can supply forged PKCS#12 files that would be accepted with PBMAC1 and short HMAC keys (1 in 256 probability).
Event History
Frequently Asked Questions
What is the severity of CVE-2026-34181?
The severity of CVE-2026-34181 is high with a CVSS score of 7.4.
How do I fix CVE-2026-34181?
To fix CVE-2026-34181, update your OpenSSL software to the latest version that addresses this vulnerability.
What impact does CVE-2026-34181 have on my systems?
CVE-2026-34181 allows an attacker to impersonate a user and potentially forge certificates and private keys.
Which software is affected by CVE-2026-34181?
CVE-2026-34181 affects the OpenSSL software library.
Is input validation sufficient in OpenSSL regarding CVE-2026-34181?
No, input validation is insufficient in OpenSSL for handling PKCS#12 files using PBMAC1, allowing exploitation.