Executive brief
A security flaw in the wolfSSL library's OpenSSL compatibility layer allows attackers to bypass certificate verification. By using a specially crafted certificate chain, an attacker can impersonate any website or service, potentially leading to intercepted communications or unauthorized access. This affects applications that use wolfSSL to handle secure connections, such as nginx or HAProxy web servers.
Technical details
A vulnerability exists in the wolfSSL_X509_verify_cert function within the OpenSSL compatibility layer. The root cause is a failure to check the leaf certificate's signature if an attacker provides an untrusted intermediate certificate with the Basic Constraints 'CA:FALSE' that is signed by a trusted root. An attacker with a valid leaf certificate from a trusted CA can forge a new certificate for any subject name and public key. This issue specifically affects the compatibility API and does not impact the native wolfSSL TLS handshake path. The vulnerability was addressed in version 5.9.1.
Affected products
- wolfSSL wolfSSL up to and including 5.9.0
Timeline
- 2026-03-30: other: Fixes submitted via pull request
- 2026-04-06: patched: Fixes merged into master branch
- 2026-04-10: disclosed: CVE-2026-5501 published