CVE-2026-55964
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
Vulnerability in the WolfSSL library involves accepting intermediate certificates with CA:TRUE but without the keyCertSign key usage as signing CAs. Previously, temporary CAs added during certificate path building (WOLFSSL_TEMP_CA) were exempt from this check, allowing invalid certificates to be accepted. Now the check applies to temporary CAs as well, except for operator-loaded root certificates (WOLFSSL_USER_CA) and self-signed ones.
Risk Assessment
The risk is the potential use of an invalid intermediate certificate to sign other certificates, which could compromise trust in the certificate chain and enable man-in-the-middle attacks or impersonation of trusted entities.
Recommendation
It is recommended to update the WolfSSL library to a version where this check is fixed. If not possible, enable the ALLOW_INVALID_CERTSIGN option only in justified cases and after a thorough risk analysis.
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Original NVD description (English source)
Chain intermediate CA:TRUE without keyCertSign accepted as a signing CA. Intermediate CA certificates are required to have the keyCertSign key usage when a Key Usage extension is present, but chain-supplied temporary CAs (WOLFSSL_TEMP_CA) added while building a certificate path were previously exempted from this check, so an intermediate asserting CA:TRUE but lacking keyCertSign was accepted as a signing CA. The check now applies to chain-supplied temporary CAs as well; only operator-loaded root certificates (WOLFSSL_USER_CA) and self-signed roots remain exempt. Per RFC 5280 an absent Key Usage extension implies all usages, so the requirement is enforced only when the extension is actually present (extKeyUsageSet). Affects the OpenSSL-compatibility certificate-path-building path (X509_verify_cert / X509_STORE, OPENSSL_EXTRA/OPENSSL_ALL), where untrusted chain intermediates are added as temporary CAs; native (non-OpenSSL-compat) certificate verification does not create temporary CAs and is unaffected. Within those builds, the check applies unless ALLOW_INVALID_CERTSIGN is defined.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS