Executive brief
openHiTLS is a cryptographic library used to secure TLS communications. A flaw in its X.509 certificate chain verification allows an attacker to bypass critical security checks by using version 1 or 2 intermediate certificates, which are not properly validated for their CA authority and basic constraints. This could enable unauthorized certificate issuance or man-in-the-middle attacks.
Technical details
The vulnerability exists in openHiTLS's X.509 certificate chain verification logic, which only validates the basic constraints extension and CA flag for version 3 (v3) certificates during intermediate CA verification. Version 1 and version 2 certificates skip these checks entirely, violating RFC 5280 certificate validation requirements. An attacker can present a crafted certificate chain using a v1/v2 intermediate certificate without proper CA authorization to bypass validation checks. The fix hardens verification by rejecting non-v3 intermediate certificates and enforcing stricter extension parsing and security level integration. Patches have been applied in pull requests #1399 (for openhitls-0.3 branch) and #1657 (for openhitls-0.2 branch).
Affected products
- openHiTLS openHiTLS 0.2.0 through 0.3.2
Timeline
- 2026-08-18: disclosed
- 2026-05-13: patched: PR #1399 closed (openhitls-0.3 branch)