Executive brief
wolfSSL is a security library used to protect data and verify identities in embedded devices and cloud applications. A flaw in how it validates digital certificates could allow a specially crafted certificate to be accepted as a trusted authority even if it lacks the proper permissions. This could potentially allow an attacker to bypass certain security checks when the library is used in a specific compatibility mode.
Technical details
A vulnerability in wolfSSL's certificate path building logic allows an intermediate certificate asserting 'CA:TRUE' to be accepted as a signing CA even if it lacks the 'keyCertSign' Key Usage extension. This violates RFC 5280 requirements which mandate this extension for intermediate CAs when a Key Usage extension is present. The issue specifically affects the OpenSSL-compatibility layer (X509_verify_cert / X509_STORE) where untrusted chain intermediates are added as temporary CAs (WOLFSSL_TEMP_CA). Native certificate verification is unaffected. An attacker could potentially use a malformed intermediate certificate to sign other certificates that the library would then incorrectly trust. The issue is resolved in version 5.9.1.
Affected products
- wolfSSL wolfSSL 5.7.4 to 5.9.1
Timeline
- 2026-06-16: patched: Fix merged in pull request 10702
- 2026-06-25: disclosed: CVE published