GoAhead CRL check skip lets revoked client certificates pass mutual TLS
Original title: Critical GoAhead Web Server Flaw Allows Attackers to Bypass Client Certificate Authentication
CVE-2026-115881 scores 9.1 on GoAhead 3.4.5–6.1.0 with mutual TLS and a loaded CRL; 6.1.1 fixes it.
FoxIO and Embedthis disclosed three TLS bugs in GoAhead. In CVE-2026-115881 the OpenSSL backend loads a CRL but never sets X509_V_FLAG_CRL_CHECK, so a revoked, previously trusted client certificate and private key can still complete mutual TLS. A LibreSSL issue lets overlong chains bypass the depth limit, and an Mbed TLS bug shrinks a Diffie-Hellman modulus so a passive observer may decrypt some TLS 1.2 DHE_RSA sessions. GoAhead 6.1.1 fixes the flaws.
Unconfirmed: FoxIO’s figure of hundreds of millions of devices is not a count of vulnerable systems.
- The OpenSSL CRL bug affects GoAhead 3.4.5 through 6.1.0 and scores CVSS 9.1.
- GOAHEAD-SA-2026-0004 scores 7.4 on LibreSSL builds 3.2.x or 3.3.2 through 3.3.6.
- GOAHEAD-SA-2026-0005 scores 5.9 on Mbed TLS builds from 4.0.2 through 6.1.0.
- TLS 1.3 and ECDHE sessions are unaffected by the weak Diffie-Hellman parameters.
- Embedthis made 6.1.1 available to device builders on August 2, 2026.
Impact: Revoked client certificates complete mutual TLS and keep access
| Product | Affected | Fixed in |
|---|---|---|
| Embedthis GoAhead | 3.4.5 through 6.1.0 with mutual TLS and a loaded CRL | 6.1.1 |
| Embedthis GoAhead | LibreSSL legacy verifier builds 3.2.x or 3.3.2 through 3.3.6 | 6.1.1 |
| Embedthis GoAhead | Mbed TLS builds 4.0.2 through 6.1.0 | 6.1.1 |
- 1.Rebuild and ship device firmware with GoAhead 6.1.1 or later.
- 2.Disable finite-field DHE suites on affected Mbed TLS builds until patched.
- 3.Enable issuer verification with a trusted CA bundle on affected LibreSSL builds.
- CVEs
- CVE-2026-115881
Vulnerabilities mentioned
All| CVE | Vulnerability | CVSS | EPSS | Signals | Published |
|---|---|---|---|---|---|
| CVE-2026-115881 | — | — | — |
From the original article
2 min read at gbhackers.com
A critical flaw in the GoAhead embedded web server lets revoked client certificates pass authentication checks, potentially restoring access to identities administrators have blocked. Tracked as CVE-2026-115881, the vulnerability carries a CVSS score of 9. 1 and affects GoAhead 3.
By Divya · gbhackers.com
A short excerpt; the article and its images belong to the publisher. Summary, key facts and assessment above are AI-written from the article and can be wrong.