FoxIO details three TLS bugs in GoAhead web server

FoxIO researcher Sébastien Féry disclosed three independent flaws in the TLS integrations of GoAhead, an embedded web server used in device-management interfaces. Exposure depends on the TLS backend and verification settings compiled into each device; the product’s large installed base does not mean every deployment is vulnerable.

In OpenSSL-compatible builds of GoAhead 3.4.5 through 6.1.0, a configured certificate revocation list is loaded but never enforced. A revoked, CA-signed client certificate can therefore complete mutual TLS even with issuer verification enabled. FoxIO identifies this as CVE-2026-115881 (GOAHEAD-SA-2026-0006), rated 9.1 by EmbedThis.

A separate chain-depth bypass, CVE-2026-115884 (GOAHEAD-SA-2026-0004, rated 7.4), affects GoAhead 6.1.0 and earlier using LibreSSL’s legacy verifier in versions 3.2.x or 3.3.2–3.3.6, when client certificates are required but issuer checking is disabled. An attacker-controlled chain longer than the configured limit can be accepted.

The Mbed TLS flaw, GOAHEAD-SA-2026-0005 (rated 5.9; no CVE assigned), affects GoAhead 4.0.2 through 6.1.0. A buffer-length typo reduces a 2048-bit Diffie–Hellman modulus to one byte. A passive observer can decrypt TLS 1.2 DHE_RSA sessions only when the client accepts those malformed parameters; TLS 1.3 and ECDHE sessions are unaffected. GoAhead 6.1.1 fixes all three flaws.

Interim options include disabling finite-field DHE suites for Mbed TLS builds and enabling issuer verification with a trusted CA bundle for affected LibreSSL builds. Device operators need firmware incorporating the fix from their device vendor.