--- 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. Two 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. Two 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' --- ## Overview 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. Two 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): First, 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. Second, 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. The 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. This 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. ## 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` ## Remediation Upgrade past the affected range: - `erlang/otp 29.0.1` ## Vendor advisories - **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) - **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) - **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) - **RHSA-2026:63160** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:63160)