nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification_CVE-2026-42790

{
    "lastseen": "",
    "description": "Improper 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.",
    "published": "2026-05-27T15:09:01.860Z",
    "modified": "2026-05-27T15:41:09.137Z",
    "type": "cve",
    "title": "nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification",
    "source": "EEF",
    "references": "https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447\nhttps://cna.erlef.org/cves/CVE-2026-42790.html\nhttps://osv.dev/vulnerability/EEF-CVE-2026-42790\nhttps://www.erlang.org/doc/system/versions.html#order-of-versions\nhttps://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759\nhttps://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457\nhttps://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a",
    "id": "CVE-2026-42790",
    "bulletinFamily": "",
    "cwe": [
        "CWE-295",
        "CWE-297"
    ],
    "cvelist": null,
    "sourceData": "Erlang OTP 1.4\nErlang OTP 19.3\nErlang OTP b0c245e8132bb13171e277b1af59c0cec00c9459",
    "sourceHref": "",
    "cvss": {
        "score": 7.6,
        "severity": "HIGH",
        "vector": "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",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "OTP",
    "version": "1.4",
    "vendor": "Erlang",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}