CVE-2026-71889

A flaw was found in Bouncy Castle. The certificate path reviewer (PKIXCertPathReviewer) fails to enforce name constraints on the end-entity certificate during validation. A remote attacker can exploit this issue by presenting a certificate that violates domain restrictions imposed by an issuing Certificate Authority (CA). Applications that rely on the reviewer to determine trust may incorrectly accept unauthorized certificates as valid.

A flaw was found in Bouncy Castle's PKIXCertPathReviewer, where X.509 name constraints are not evaluated against the end-entity certificate during path validation. An attacker can exploit this by presenting a certificate chain with a leaf certificate violating domain or subtree restrictions set by an issuing Certificate Authority. If an application relies on PKIXCertPathReviewer rather than standard CertPathValidator to determine trust decisions, it may accept unauthorized or spoofed certificates as valid, bypassing intended certificate-based authentication and integrity controls.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Do not use PKIXCertPathReviewer for trust or path validation decisions. Instead, validate certificate paths using the standard Java Cryptography Architecture via CertPathValidator.getInstance("PKIX", "BC").