EmbedThis published GitHub security advisory GHSA-5m75-xq69-c3c5 for its GoAhead embedded web server on 12 October 2026, rated Critical, saying the OpenSSL TLS backend loads a configured certificate revocation list (CRL) into the OpenSSL certificate store but never enables CRL checking, so "revoked client certificates are silently accepted" (CVE-2026-115881).

EmbedThis says exploitation requires the OpenSSL backend (the project's preferred and default TLS backend), mutual TLS with a CA bundle, issuer checking and a CRL all configured, and an attacker holding a client certificate signed by a trusted CA that is listed as revoked, such as a stolen or decommissioned device certificate; the default GoAhead build does not enable mutual TLS or load a CRL, and Mbed TLS builds are not vulnerable. Affected versions are 3.4.5 through 6.1.0 and the fix is 6.1.1.

EmbedThis published two related advisories the same day: GHSA-r392-vqwx-3r4g (CVE-2026-115884, rated High), where builds linked against LibreSSL's legacy X.509 verifier (LibreSSL 3.2.x or 3.3.2 to 3.3.6) that require client certificates without issuer checking accept an over-depth self-signed chain, and GHSA-fmvx-2xfx-2gq4 (rated Moderate), where Mbed TLS builds send a 1-byte Diffie-Hellman modulus on TLS 1.2 DHE-RSA handshakes, letting a passive observer decrypt sessions with clients that accept it.

Sébastien Féry of FoxIO, who reported the flaws, published a write-up on 26 October rating them CVSS 9.1, 7.4 and 5.9, saying GoAhead 6.1.1 was released on 2 August 2026 and that reproduction code (proof of concept) is available; FoxIO says GoAhead is used in hundreds of millions of devices.

Neither EmbedThis nor FoxIO says the flaws are exploited in the wild. Primary: EmbedThis advisories; researcher: FoxIO.