{"id":"CVE-2026-42790","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.\n\nTwo flaws combine to allow a s…","summary":"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 s…","severity":"high","cvss":8.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","cwe":["CWE-295","CWE-297"],"vendor":"erlang","product":"erlang/otp","affected":["erlang/otp >= 19.3, < 26.2.5.21","erlang/otp >= 27.0, < 27.3.4.12","erlang/otp >= 28.0, < 28.5.0.1","erlang/otp >= 29.0, < 29.0.1"],"patched":["erlang/otp 29.0.1"],"published":"2026-05-27","updated":"2026-09-18","sourceUpdated":"2026-09-18T13:18:22.680","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-42790","references":[{"url":"https://cna.erlef.org/cves/CVE-2026-42790.html","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-42790","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://www.erlang.org/doc/system/versions.html#order-of-versions","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://access.redhat.com/errata/RHSA-2026:39809","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/errata/RHSA-2026:54757","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/security/cve/CVE-2026-42790","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2482286","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42790.json","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-42790"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42790"},{"url":"https://access.redhat.com/errata/RHSA-2026:63160"}],"tags":["nvd","csaf","vex","red-hat","cve.org"],"epss":0.00338,"epssPercentile":0.2728,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-05-27T00:00:00+00:00"},"scores":{"nvd":8.1,"vendor":7.4,"cna":7.6},"ingestedAt":"2026-07-16T02:48:54.993Z","slug":"CVE-2026-42790","body":"## Overview\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 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.\n\n## Affected\n\n- `erlang/otp >= 19.3, < 26.2.5.21`\n- `erlang/otp >= 27.0, < 27.3.4.12`\n- `erlang/otp >= 28.0, < 28.5.0.1`\n- `erlang/otp >= 29.0, < 29.0.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `erlang/otp 29.0.1`\n\n## Vendor advisories\n\n- **RHSA-2026:54757** · Red Hat · fixed in: Red Hat OpenStack Platform 16.2 · released 2026-08-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:54757)\n- **RHSA-2026:39809** · Red Hat · fixed in: Red Hat OpenStack Services on OpenShift 18.0 · released 2026-07-15 · [advisory](https://access.redhat.com/errata/RHSA-2026:39809)\n- **Red Hat VEX** · Important · affected: Red Hat OpenStack Platform 17.1 · no fix planned: Red Hat OpenStack Platform 17.1 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42790.json)\n- **RHSA-2026:63160** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:63160)","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":44.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}