{"cvss":7.6,"datePublished":"2026-05-27T17:16:36.030","dateUpdated":"2026-09-18T13:18:22.680","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.","id":"CVE-2026-42790","raw":{"affected":[{"affectedData":[{"cpes":["cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"],"defaultStatus":"unknown","modules":["pubkey_cert","public_key"],"packageName":"public_key","packageURL":"pkg:otp/public_key?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp&vcs_url=git%20https:%2F%2Fgithub.com%2Ferlang%2Fotp.git","product":"OTP","programFiles":["src/pubkey_cert.erl","src/public_key.erl"],"programRoutines":[{"name":"pubkey_cert:validate_names/6"},{"name":"public_key:pkix_verify_hostname/3"}],"repo":"https://github.com/erlang/otp","vendor":"Erlang","versions":[{"changes":[{"at":"1.15.1.7","status":"unaffected"},{"at":"1.17.1.3","status":"unaffected"},{"at":"1.20.3.1","status":"unaffected"},{"at":"1.21.1","status":"unaffected"}],"lessThan":"*","status":"affected","version":"1.4","versionType":"otp"}]},{"collectionURL":"https://github.com","cpes":["cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"],"defaultStatus":"unknown","modules":["pubkey_cert","public_key"],"packageName":"erlang/otp","packageURL":"pkg:github/erlang/otp","product":"OTP","programFiles":["lib/public_key/src/pubkey_cert.erl","lib/public_key/src/public_key.erl"],"programRoutines":[{"name":"pubkey_cert:validate_names/6"},{"name":"public_key:pkix_verify_hostname/3"}],"repo":"https://github.com/erlang/otp","vendor":"Erlang","versions":[{"changes":[{"at":"26.2.5.21","status":"unaffected"},{"at":"27.3.4.12","status":"unaffected"},{"at":"28.5.0.1","status":"unaffected"},{"at":"29.0.1","status":"unaffected"}],"lessThan":"*","status":"affected","version":"19.3","versionType":"otp"},{"changes":[{"at":"0769050c69d73762672b0db1347b6993a5b31759","status":"unaffected"},{"at":"fb67c6d1836f51105a96d8b769e71e4215a79457","status":"unaffected"},{"at":"21abed64eb2026b5f82f432709e4e932f9be389a","status":"unaffected"}],"lessThan":"*","status":"affected","version":"b0c245e8132bb13171e277b1af59c0cec00c9459","versionType":"git"}]}],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"affectedData":[{"collectionURL":"https://access.redhat.com/downloads/content/package-browser/","cpes":["cpe:/a:redhat:openstack:16.2::el8"],"defaultStatus":"affected","packageName":"erlang","product":"Red Hat OpenStack Platform 16.2","vendor":"Red Hat","versions":[{"lessThan":"*","status":"unaffected","version":"0:23.3.4.18-2.el8ost","versionType":"rpm"}]},{"collectionURL":"https://access.redhat.com/downloads/content/package-browser/","cpes":["cpe:/a:redhat:openstack:18.0::el9"],"defaultStatus":"affected","packageName":"erlang","product":"Red Hat OpenStack Services on OpenShift 18.0","vendor":"Red Hat","versions":[{"lessThan":"*","status":"unaffected","version":"0:26.2.5.21-2.el9ost","versionType":"rpm"}]},{"collectionURL":"https://access.redhat.com/downloads/content/package-browser/","cpes":["cpe:/a:redhat:hummingbird:1"],"defaultStatus":"affected","packageName":"erlang27","product":"Red Hat Hardened Images","vendor":"Red Hat"},{"collectionURL":"https://access.redhat.com/downloads/content/package-browser/","cpes":["cpe:/a:redhat:openstack:17.1"],"defaultStatus":"affected","packageName":"erlang","product":"Red Hat OpenStack Platform 17.1","vendor":"Red Hat"}],"source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"}],"configurations":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*","matchCriteriaId":"245CC08C-EB1F-4230-8F4B-98CFFB623EB2","versionEndExcluding":"26.2.5.21","versionStartIncluding":"19.3","vulnerable":true},{"criteria":"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*","matchCriteriaId":"91269F6D-B8A3-41F2-871C-79EBB9460BE8","versionEndExcluding":"27.3.4.12","versionStartIncluding":"27.0","vulnerable":true},{"criteria":"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*","matchCriteriaId":"844A3F01-AF3C-4C48-81DB-932B803D22C4","versionEndExcluding":"28.5.0.1","versionStartIncluding":"28.0","vulnerable":true},{"criteria":"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*","matchCriteriaId":"46976598-817C-4E93-AC4B-46434746C25F","versionEndExcluding":"29.0.1","versionStartIncluding":"29.0","vulnerable":true}],"negate":false,"operator":"OR"}]}],"cveTags":[],"descriptions":[{"lang":"en","value":"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."}],"id":"CVE-2026-42790","lastModified":"2026-09-18T13:18:22.680","metrics":{"cvssMetricV31":[{"cvssData":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","version":"3.1"},"exploitabilityScore":2.8,"impactScore":5.2,"source":"nvd@nist.gov","type":"Primary"},{"cvssData":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":7.4,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","version":"3.1"},"exploitabilityScore":2.2,"impactScore":5.2,"source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c","type":"Secondary"}],"cvssMetricV40":[{"cvssData":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"HIGH","attackRequirements":"PRESENT","attackVector":"NETWORK","availabilityRequirement":"NOT_DEFINED","baseScore":7.6,"baseSeverity":"HIGH","confidentialityRequirement":"NOT_DEFINED","exploitMaturity":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"PASSIVE","valueDensity":"NOT_DEFINED","vectorString":"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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnerabilityResponseEffort":"NOT_DEFINED"},"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","type":"Secondary"}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"id":"CVE-2026-42790","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"role":"CISA Coordinator","timestamp":"2026-05-27T00:00:00+00:00","version":"2.0.3"}}]},"published":"2026-05-27T17:16:36.030","references":[{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Third Party Advisory"],"url":"https://cna.erlef.org/cves/CVE-2026-42790.html"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Patch"],"url":"https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Patch"],"url":"https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Patch"],"url":"https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Vendor Advisory"],"url":"https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Mitigation","Third Party Advisory"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-42790"},{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":["Product"],"url":"https://www.erlang.org/doc/system/versions.html#order-of-versions"},{"source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c","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"}],"sourceIdentifier":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","vulnStatus":"Modified","weaknesses":[{"description":[{"lang":"en","value":"CWE-295"},{"lang":"en","value":"CWE-297"}],"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","type":"Secondary"},{"description":[{"lang":"en","value":"CWE-295"}],"source":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c","type":"Secondary"}]},"severity":"HIGH","source":"nvd","title":"Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a ..."}