High 7.6Published May 27, 2026

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

Updated under an hour ago (Oct 27, 2026, 10:10 AM ET)

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Exploited in the last 30 days

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.

CVSS: 7.6 HIGH (v4.0, CNA)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
Weakness (CWE): CWE-295, CWE-297
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: EEF
NVD analysis: Modified
Record last updated: Sep 18, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Erlang OTP erlang:erlang/otp	from 1.4; fixed at 1.15.1.7, fixed at 1.17.1.3, fixed at 1.20.3.1, fixed at 1.21.1	CNA record
Red Hat Red Hat OpenStack Platform 16.2 redhat:openstack	from 0:23.3.4.18-2.el8ost not affected	CISA ADP
Red Hat Red Hat Hardened Images redhat:hummingbird	1	CISA ADP
erlang erlang/otp erlang:erlang/otp	from 19.3 before 26.2.5.21; from 27.0 before 27.3.4.12; from 28.0 before 28.5.0.1; from 29.0 before 29.0.1	NVD

References

References

https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447	vendor-advisory, related
https://cna.erlef.org/cves/CVE-2026-42790.html	related, third-party-advisory
https://osv.dev/vulnerability/EEF-CVE-2026-42790	related, mitigation, third-party-advisory
https://www.erlang.org/doc/system/versions.html#order-of-versions	x-version-scheme, product
https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759	patch
https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457	patch
https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a	patch
https://access.redhat.com/errata/RHSA-2026:39809
https://access.redhat.com/errata/RHSA-2026:54757
https://access.redhat.com/security/cve/CVE-2026-42790
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.