FoxIO finds three TLS flaws in widely used GoAhead server

FoxIO has disclosed three vulnerabilities in GoAhead’s TLS handling, affecting a GoAhead Web Server used in hundreds of millions of devices across IoT, OT, firewall, and military sectors. The flaws, attributed to the TLS implementation in GoAhead, can allow a revoked client certificate to continue to be trusted, enable eavesdroppers to decrypt some TLS traffic, or bypass a certificate chain length limit. The impact depends on the TLS library bundled in the firmware and how certificate checks are configured.

The most severe issue, CVE-2026-115881 (CVSS 9.1), affects GoAhead versions 3.4.5 to 6.1.0 when built with OpenSSL or a compatible library and configured for mutual TLS with a certificate revocation list, because the server reads the revocation list but never consults it with OpenSSL. A second bug (CVSS 5.9, no CVE) affects GoAhead 4.0.2 to 6.1.0 with Mbed TLS, where a coding error can weaken certain TLS 1.2 connections enough to decrypt recorded sessions offline, subject to client parameter acceptance.

The third flaw, CVE-2026-115884 (CVSS 7.4), involves LibreSSL 3.2.x or 3.3.2–3.3.6 on GoAhead up to 6.1.0 and allows bypassing the chain-length cap when client certificates are accepted from any issuer. GoAhead 6.1.1, released on 2 Aug, fixes the OpenSSL and Mbed TLS issues; advisories were issued on 12 Oct. FoxIO also released PoC code and device fingerprints to help defenders identify exposed GoAhead servers and their TLS backends.