{"affected":[{"ranges":[{"events":[{"introduced":"b0c245e8132bb13171e277b1af59c0cec00c9459"},{"fixed":"0769050c69d73762672b0db1347b6993a5b31759"},{"fixed":"fb67c6d1836f51105a96d8b769e71e4215a79457"},{"fixed":"21abed64eb2026b5f82f432709e4e932f9be389a"}],"repo":"https://github.com/erlang/otp","type":"GIT"}]}],"aliases":["GHSA-22cw-4ph4-6447","CVE-2026-42790"],"credits":[{"name":"John Downey","type":"FINDER"},{"name":"Ingela Anderton Andin","type":"REMEDIATION_DEVELOPER"},{"name":"Dan Gudmundsson","type":"REMEDIATION_REVIEWER"},{"name":"Jakub Witczak","type":"REMEDIATION_REVIEWER"}],"database_specific":{"capec_ids":["CAPEC-475"],"cpe_ids":["cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-295","CWE-297"]},"details":"## Summary\n\nImproper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification.\n\nTwo flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com):\n\nFirst, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName.\n\nSecond, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback.\n\nThe result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher.\n\nThis issue affects OTP from OTP 19.3 before OTP 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.\n\n## Workaround\n\nThe verify_fun option in the ssl application can be used to ensure that TLS connections fail if the end-entity certificate is missing the subjectAltName extension or has no domain name. Do not use a verify_fun that accepts the name_not_permitted error.","id":"EEF-CVE-2026-42790","modified":"2026-05-27T15:41:09.137Z","published":"2026-05-27T15:09:01.860Z","references":[{"type":"ADVISORY","url":"https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-42790.html"},{"type":"WEB","url":"https://www.erlang.org/doc/system/versions.html#order-of-versions"},{"type":"FIX","url":"https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759"},{"type":"FIX","url":"https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457"},{"type":"FIX","url":"https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","type":"CVSS_V4"}],"summary":"nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification","upstream":[]}