Platform
c
Component
wolfssl
Fixed in
5.9.1
CVE-2026-5263 affects wolfSSL versions 0.0.0 through 5.9.1. This vulnerability arises from the improper enforcement of nameConstraints during certificate chain verification. Consequently, a compromised or malicious sub-Certificate Authority (CA) could issue leaf certificates with URI Subject Alternative Name (SAN) entries that violate the constraints imposed by the issuing CA, leading wolfSSL to incorrectly validate them as legitimate. The vulnerability was published on 2026-04-09, and a fix is available in version 5.9.1.
The core impact of CVE-2026-5263 lies in the potential for man-in-the-middle (MITM) attacks and the acceptance of fraudulent certificates. An attacker controlling a sub-CA could issue certificates for arbitrary domains, effectively impersonating legitimate services. This could lead to data breaches, credential theft, and the execution of malicious code. The blast radius is significant, potentially impacting any application or system relying on wolfSSL for certificate validation. This vulnerability shares similarities with other certificate validation bypasses, where improper constraint enforcement allows for the acceptance of invalid certificates, potentially leading to similar consequences.
CVE-2026-5263 is not currently listed on KEV. The EPSS score is pending evaluation. No public proof-of-concept (PoC) exploits are currently known. The vulnerability was publicly disclosed on 2026-04-09.
Exploit Status
EPSS
0.03% (7% percentile)
CISA SSVC
The primary mitigation for CVE-2026-5263 is to upgrade to wolfSSL version 5.9.1 or later, which includes the necessary fix. If upgrading is not immediately feasible, consider implementing stricter certificate pinning policies within your applications to limit the set of trusted certificates. While not a complete solution, this can reduce the attack surface. Review your certificate chain validation logic to ensure it adheres to best practices and properly enforces nameConstraints. After upgrading, confirm the fix by performing a test with a certificate that previously would have been incorrectly validated, ensuring it is now rejected.
Update to version 5.9.1 or later of wolfSSL to mitigate the vulnerability. This update corrects the failure to enforce URI name constraints in certificate chains, preventing malicious certificates from being accepted.
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CVE-2026-5263 is a vulnerability in wolfSSL affecting versions 0.0.0–5.9.1 where nameConstraints are not enforced during certificate validation, allowing potentially malicious certificates to be accepted.
If you are using wolfSSL versions 0.0.0 through 5.9.1 and rely on certificate chain validation, you are potentially affected by this vulnerability.
Upgrade to wolfSSL version 5.9.1 or later to address this vulnerability. Consider implementing certificate pinning as an interim measure.
As of the current date, there are no confirmed reports of active exploitation of CVE-2026-5263.
Refer to the official wolfSSL security advisory for detailed information and updates regarding CVE-2026-5263.
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