GoAhead, a small web server that device makers build into firmware for management pages on routers, printers, gateways and industrial controllers, has three TLS flaws, according to FoxIO researcher Sébastien Féry and The Hacker News. The most serious, CVE-2026-115881 (rated 9.1 by the vendor, EmbedThis), affects the default OpenSSL backend. The server loads a certificate revocation list at startup without error but never turns revocation checking on, so a revoked client certificate, for example from a stolen or retired device, still completes the handshake. It only matters on builds that require client certificates, have a trusted CA bundle and issuer checking enabled, and have a revocation list configured.
The other two depend on the TLS library compiled into the firmware. On older LibreSSL versions (3.2.x and 3.3.2 to 3.3.6) with client certificates required and issuer checking off, a certificate chain longer than GoAhead’s limit of 10 is accepted (CVE-2026-115884, rated 7.4). On the Mbed TLS backend, a length typo makes the server send a 1-byte Diffie-Hellman value, so someone who recorded a session could decrypt it if the client accepts the weak value; this one has no CVE yet and a 5.9 rating. The Hacker News says that mainstream clients such as browsers refuse the small value, and that TLS 1.3 and ECDHE sessions are unaffected. GoAhead 6.1.1 fixes all three. As of 27 October, The Hacker News says no attacks had been reported, and the CVE ids were not yet live in the public CVE and NVD databases. Ratings are the vendor’s own.
How to check if you’re affected
Affected versions are GoAhead 3.4.5 through 6.1.0 with the OpenSSL backend for CVE-2026-115881, 6.1.0 and earlier on the LibreSSL versions above for CVE-2026-115884, and 4.0.2 through 6.1.0 on Mbed TLS for the third flaw, per The Hacker News. Which backend and settings a device uses are chosen when the firmware is built, so an owner usually cannot tell from the outside.
- If you build firmware on GoAhead, upgrade to 6.1.1. For the LibreSSL issue the advisory also allows turning issuer checking on with a trusted CA bundle, or moving to OpenSSL or LibreSSL 4.x. For the Mbed TLS issue, turn off finite-field DHE suites or use the OpenSSL backend.
- If you own an affected device, there is no owner-side fix: 6.1.1 reaches you only when the manufacturer ships a firmware update, and The Hacker News says it is not known whether any manufacturer has. Check your vendor’s security notices and keep management pages off the public internet.
- If your devices use mutual TLS with a revocation list, treat revoked certificates as still usable until the firmware is patched, and rotate or remove access that depended on them where you can.
Sources
- GHSA-5m75-xq69-c3c5: OpenSSL CRL loaded but not enforced in GoAhead (CVE-2026-115881)
- GHSA-r392-vqwx-3r4g: mTLS client-certificate bypass on LibreSSL legacy verifier (CVE-2026-115884)
- GHSA-fmvx-2xfx-2gq4: Mbed TLS DH parameter truncation
- GoAhead v6.1.1 release
- FoxIO: Choose your backend, three TLS bugs in GoAhead
- The Hacker News: GoAhead TLS Flaws Allow Revoked Client Certificates and Enable Session Decryption