Vulnerability · Published Oct 30, 2026 · Assigned by EEF

CVE-2026-117666ssl_verify_fun: partial-label wildcard certificate matches hostnames across a label boundary

Critical 9.1

In plain English

A critical-severity security flaw in ssl_verify_fun from deadtrickster. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities).

Severity (CVSS 4.0)9.1Critical

Exploit odds (30 days)0.2%top 91.3% of all CVEs

Exploited in the wildNo reportsnot in CISA KEV

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	rebar3	no fix listed	DEBIAN-CVE-2026-117666
Debian:13	rebar3	no fix listed	DEBIAN-CVE-2026-117666
Debian:14	rebar3	no fix listed	DEBIAN-CVE-2026-117666

Affected products (as reported)

Vendor	Product	Versions
deadtrickster	ssl_verify_fun	1.0.1 – before 1.1.8
deadtrickster	ssl_verify_fun	a49ca56923356c7a3981692b23c42ef32c2990e0 – before ca34031299cd2e0c98794c0da4ba556b94e39aad

Weakness: CWE-297 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

References

ssl_verify_fun: partial-label wildcard certificate matches hostnames across a label boundary vendor-advisory, related
EEF CNA record for CVE-2026-117666 related
OSV record EEF-CVE-2026-117666 related
Do not let partial-label wildcards match across label boundaries (ssl_verify_fun.erl pull request #33) patch
Introducing commit a49ca56 in deadtrickster/ssl_verify_fun.erl related
Fix commit ca34031 in deadtrickster/ssl_verify_fun.erl patch