Improper Validation of Certificate with Host Mismatch vulnerability in deadtrickster ssl_verify_fun…

Why it is Yellow

• CVSS 9.1 critical
• Remotely exploitable without logging in

References

• https://cna.erlef.org/cves/CVE-2026-117666.html
• https://github.com/deadtrickster/ssl_verify_fun.erl/commit/a49ca56923356c7a3981692b23c42ef32c2990e0
• https://github.com/deadtrickster/ssl_verify_fun.erl/commit/ca34031299cd2e0c98794c0da4ba556b94e39aad
• https://github.com/deadtrickster/ssl_verify_fun.erl/pull/33
• https://github.com/deadtrickster/ssl_verify_fun.erl/security/advisories/GHSA-7gw2-hphm-c5px
• https://osv.dev/vulnerability/EEF-CVE-2026-117666

Original description

Improper Validation of Certificate with Host Mismatch vulnerability in deadtrickster ssl_verify_fun allows an adversary in the middle to impersonate a TLS peer via a certificate that carries a partial-label wildcard. try_match_wildcard/4 in src/ssl_verify_hostname.erl anchors only the text before and after the * of an identifier such as f*.example.net, so the wildcard also consumes dots and the certificate is accepted for f.evil.example.net. RFC 6125 confines a wildcard to the left-most label. The same matcher lets *.168.1.1 match the IP literal 192.168.1.1. Whole-label wildcards are matched correctly. Erlang/OTP 20.0 and later check the hostname in ssl before a user verify_fun sees valid_peer, so a client that keeps server_name_indication set rejects the mismatch regardless. Exposed are clients that disable SNI, servers that verify client certificate hostnames with this library, and direct callers of verify_cert_hostname/2. This issue affects ssl_verify_fun: from 1.0.1 before 1.1.8.