CVE-2026-105236: Cert Validation Flaw

Description

Improper Certificate Validation vulnerability in the ssl application in Erlang/OTP allows a client that holds a certificate trusted by one SNI virtual host to authenticate to a second SNI virtual host on the same listener by resuming its TLS 1.2 session there. A server that serves several SNI names from one listen socket through sni_fun or sni_hosts keeps one pre-TLS 1.3 session cache per listener and does not bind a cached session to the SNI name or client trust policy that established it. When an SNI option set switches to verify_peer without naming reuse_sessions, ssl_config:update_options/3 inherits the base listener's reuse_sessions value of true, so the default that disables reuse for client-authenticating servers does not apply. On an abbreviated handshake ssl_session:is_resumable/4 checks only that the cached session uses one of the current server certificates and carries some peer certificate, and never revalidates that certificate against the CA selected for the requested name. The names must share a server certificate, which is common with wildcard or multi-SAN certificates. TLS 1.3 does not use this cache and is not affected. This issue affects OTP from OTP 18.0 before OTP 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to ssl from 7.0 before 11.2.12.14, 11.6.0.7, and 11.7.8.

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Weakness Type (CWE)

CWE-295 CWE-295

References

Other References

https://cna.erlef.org/cves/CVE-2026-105236.html https://github.com/erlang/otp/commit/0c20f3683b3c81fd30b46047195be9b3d2c69d76 https://github.com/erlang/otp/commit/10ee925d0fee8413f1170cc21bfcf123c8d22454 https://github.com/erlang/otp/commit/4d76adbf39d547a931048544df09c3c087e56618 https://github.com/erlang/otp/commit/4fe38c4b8b2c8024afb60990e598ff823743fd54 https://github.com/erlang/otp/security/advisories/GHSA-2g23-cgjh-34gq https://osv.dev/vulnerability/EEF-CVE-2026-105236 https://www.erlang.org/doc/system/versions.html#order-of-versions

Frequently Asked Questions

What is CVE-2026-105236? +

Improper Certificate Validation vulnerability in the ssl application in Erlang/OTP allows a client that holds a certificate trusted by one SNI virtual host to authenticate to a second SNI virtual host on the same listener by resuming its TLS 1.2 session there. A server that serves several SNI names from one listen socket through sni_fun or sni_hosts keeps one pre-TLS 1.3 session cache per listener and does not bind a cached session to the SNI name or client trust policy that established it. When an SNI option set switches to verify_peer without naming reuse_sessions, ssl_config:update_options/3 inherits the base listener's reuse_sessions value of true, so the default that disables reuse for client-authenticating servers does not apply. On an abbreviated handshake ssl_session:is_resumable/4 checks only that the cached session uses one of the current server certificates and carries some peer certificate, and never revalidates that certificate against the CA selected for the requested name. The names must share a server certificate, which is common with wildcard or multi-SAN certificates. TLS 1.3 does not use this cache and is not affected. This issue affects OTP from OTP 18.0 before OTP 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to ssl from 7.0 before 11.2.12.14, 11.6.0.7, and 11.7.8.

How do I check if I'm vulnerable to CVE-2026-105236? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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