The default TLS certificate validator in Envoy incorrectly converts a DNS SAN string containing an embedded NUL byte into a C‑style string, causing the string to be truncated by strlen() before algorithm evaluates it. As a result, a certificate with a forged dNSName that includes a NUL byte satisfies the required San match and is accepted as valid. This flaw enables an attacker to bypass the intended certificate validation and gain unauthorized access or impersonate upstream services. The vulnerability is a forgery of the certificate authentication process rather than a memory corruption or denial of service.

All Envoy releases prior to , 1.36.7, 1.37.3, and 1.38.1 are affected. Versions 1.35.0‑1.35.10, 1.36.0‑1.36.6, 1.37.0‑1.37.2, and 1.38.0 are vulnerable until the specified patch releases are installed.

The CVSS score of 4.4 indicates moderate severity, and the EPSS score is not available, so the overall exploitation probability is uncertain. Because the flaw lies in the server‑side certificate validation logic, an attacker would need control over the TLS handshake between Envoy and an upstream service to supply a malicious certificate. The vulnerability is not listed inV catalog, and no public exploits have been reported. If Envoy functions as a gateway to untrusted upstream services, the risk rises, but the lack of publicly demonstrated exploits mitigates immediate concern.