{"id":"CVE-2026-42790","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-42790","generatedAt":"2026-10-28T10:46:52.655Z","title":"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.","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 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.","published":"2026-05-27T17:16:36.000Z","lastModified":"2026-10-26T11:10:00.000Z","status":"Modified","sourceIdentifier":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","cvss":{"version":"4.0","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-295","CWE-297"],"affected":["erlang/erlang\\/otp"],"epss":{"score":0.00345,"percentile":0.27932,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.34%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-42790.html","tags":["Third Party Advisory"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759","tags":["Patch"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a","tags":["Patch"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457","tags":["Patch"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447","tags":["Vendor Advisory"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-42790","tags":["Mitigation","Third Party Advisory"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://www.erlang.org/doc/system/versions.html#order-of-versions","tags":["Product"],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://access.redhat.com/errata/RHSA-2026:39809","source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/errata/RHSA-2026:54757","source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/security/cve/CVE-2026-42790","source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2482286","source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42790.json","source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-42790","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}