GoAhead TLS Flaws Allow Revoked Client Certificates and Enable Session Decryption

Security researcher Sébastien Féry of FoxIO disclosed that the embedded GoAhead web server, used in firmware for routers, printers, gateways and industrial equipment by vendors such as HP, Siemens, Canon and D-Link, loaded certificate revocation lists without ever actually enforcing them. On builds using the OpenSSL backend with mutual-TLS and revocation checking configured, a revoked client certificate—such as one belonging to a stolen or decommissioned device—could still complete authentication and gain access, tracked as CVE-2026-115881 with a vendor-assigned severity of 9.1. Two related issues were also found: a LibreSSL-based bug (CVE-2026-115884, rated 7.4) letting attackers bypass authentication with an oversized certificate chain, and an Mbed TLS flaw (no CVE yet, rated 5.9) that sends a truncated Diffie-Hellman value, letting passive eavesdroppers decrypt sessions on non-compliant clients. EmbedThis fixed all three issues, plus eight other advisories including a critical login-bypass bug tied to Blowfish-hashed passwords, in GoAhead 6.1.1, but since device makers must rebuild and distribute firmware themselves, it's unclear which, if any, vendors have shipped the patch yet; no active exploitation has been reported so far.