Forge, a JavaScript implementation of TLS, incorrectly treated deprecated extension OIDs 2.5.29.10 and 2.5.29.13 as basicConstraints. This flaw allows an attacker to insert a permissive deprecated extension before the real basicConstraints extension in a certificate chain. When the issuer is a CA trusted by the application, the certificate can be accepted as a CA and used to issue certificates for arbitrary names, enabling server or client impersonation. The weakness is rooted in improper verification of cryptographic parameters (CWE‑295) and the use of deprecated functions (CWE‑436).

The affected product is digitalbazaar's Forge (node-forge). Any installation running a version prior to 1.4.1 is vulnerable. Users of earlier node-forge releases that rely on pki.verifyCertificateChain() for TLS/SSL verification must evaluate whether they accept certificates issued by trusted CAs that might contain the deprecated OIDs.

With a CVSS score of 7.4, the flaw is rated high severity. The EPSS score is not available, and the vulnerability is not listed in the CISA KEV catalog. Exploitation requires that an attacker control a trusted CA or influence a CA to issue a certificate carrying the deprecated extensions. Once a chain containing such a certificate is accepted, the attacker can generate a seemingly valid certificate for any domain, enabling man‑in‑the‑middle attacks or impersonation of services. The attack vector is thus limited to environments that depend on node-forge for TLS certificate validation and trust any CA that might include the deprecated extensions.