CVE-2026-42790 (GCVE-0-2026-42790)
Vulnerability from cvelistv5 – Published: 2026-05-27 15:09 – Updated: 2026-07-01 04:45
VLAI?
Title
nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification
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 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 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.
Severity ?
CWE
Assigner
References
| URL | Tags | |
|---|---|---|
|
|
||
Impacted products
Credits
John Downey
Ingela Anderton Andin
Dan Gudmundsson
Jakub Witczak
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This can lead to hostname spoofing and potential man-in-the-middle attacks, compromising the integrity and confidentiality of communications.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-295\", \"description\": \"Improper Certificate Validation\"}]}], \"providerMetadata\": {\"orgId\": \"0b0ca135-0b70-47e7-9f44-1890c2a1c46c\", \"shortName\": \"redhat-SADP\", \"dateUpdated\": \"2026-06-30T12:08:38.311Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-42790\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-05-27T17:31:50.271881Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-05-27T17:31:58.755Z\"}}], \"cna\": {\"title\": \"nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"John Downey\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Ingela Anderton Andin\"}, {\"lang\": \"en\", \"type\": \"remediation reviewer\", \"value\": \"Dan Gudmundsson\"}, {\"lang\": \"en\", \"type\": \"remediation reviewer\", \"value\": \"Jakub Witczak\"}], \"impacts\": [{\"capecId\": \"CAPEC-475\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-475 Signature Spoofing by Improper Validation\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 7.6, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"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\", \"userInteraction\": \"PASSIVE\", \"attackComplexity\": \"HIGH\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"HIGH\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"HIGH\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"pubkey_cert\", \"public_key\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"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\"}], \"version\": \"1.4\", \"lessThan\": \"*\", \"versionType\": \"otp\"}], \"packageURL\": \"pkg:otp/public_key?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp\u0026vcs_url=git%20https:%2F%2Fgithub.com%2Ferlang%2Fotp.git\", \"packageName\": \"public_key\", \"programFiles\": [\"src/pubkey_cert.erl\", \"src/public_key.erl\"], \"defaultStatus\": \"unknown\", \"programRoutines\": [{\"name\": \"pubkey_cert:validate_names/6\"}, {\"name\": \"public_key:pkix_verify_hostname/3\"}]}, {\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"pubkey_cert\", \"public_key\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"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\"}], \"version\": \"19.3\", \"lessThan\": \"*\", \"versionType\": \"otp\"}, {\"status\": \"affected\", \"changes\": [{\"at\": \"0769050c69d73762672b0db1347b6993a5b31759\", \"status\": \"unaffected\"}, {\"at\": \"fb67c6d1836f51105a96d8b769e71e4215a79457\", \"status\": \"unaffected\"}, {\"at\": \"21abed64eb2026b5f82f432709e4e932f9be389a\", \"status\": \"unaffected\"}], \"version\": \"b0c245e8132bb13171e277b1af59c0cec00c9459\", \"lessThan\": \"*\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/erlang/otp\", \"packageName\": \"erlang/otp\", \"programFiles\": [\"lib/public_key/src/pubkey_cert.erl\", \"lib/public_key/src/public_key.erl\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unknown\", \"programRoutines\": [{\"name\": \"pubkey_cert:validate_names/6\"}, {\"name\": \"public_key:pkix_verify_hostname/3\"}]}], \"references\": [{\"url\": \"https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-42790.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-42790\", \"tags\": [\"related\"]}, {\"url\": \"https://www.erlang.org/doc/system/versions.html#order-of-versions\", \"tags\": [\"x_version-scheme\"]}, {\"url\": \"https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a\", \"tags\": [\"patch\"]}], \"workarounds\": [{\"lang\": \"en\", \"value\": \"The verify_fun option in the ssl application can be used to ensure that TLS connections fail if the end-entity certificate is missing the subjectAltName extension or has no domain name. Do not use a verify_fun that accepts the name_not_permitted error.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"The \u003ctt\u003everify_fun\u003c/tt\u003e option in the \u003ctt\u003essl\u003c/tt\u003e application can be used to ensure that TLS connections fail if the end-entity certificate is missing the \u003ctt\u003esubjectAltName\u003c/tt\u003e extension or has no domain name. Do not use a \u003ctt\u003everify_fun\u003c/tt\u003e that accepts the \u003ctt\u003ename_not_permitted\u003c/tt\u003e error.\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"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 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Improper Certificate Validation vulnerability in Erlang OTP \u003ctt\u003epublic_key\u003c/tt\u003e (\u003ctt\u003epubkey_cert\u003c/tt\u003e and \u003ctt\u003epublic_key\u003c/tt\u003e modules) allows a DNS \u003ctt\u003enameConstraints\u003c/tt\u003e bypass via subject CommonName fallback in TLS hostname verification.\u003cp\u003eTwo flaws combine to allow a subordinate CA whose DNS \u003ctt\u003enameConstraints\u003c/tt\u003e are restricted (e.g. \u003ctt\u003epermitted;DNS:allowed.example.com\u003c/tt\u003e) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. \u003ctt\u003evictim.example.com\u003c/tt\u003e):\u003c/p\u003e\u003cp\u003eFirst, \u003ctt\u003epubkey_cert:validate_names/6\u003c/tt\u003e in \u003ctt\u003elib/public_key/src/pubkey_cert.erl\u003c/tt\u003e only checks SAN DNS entries against \u003ctt\u003enameConstraints\u003c/tt\u003e. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no \u003ctt\u003esubjectAltName\u003c/tt\u003e therefore trivially satisfies any \u003ctt\u003epermitted;DNS:...\u003c/tt\u003e constraint regardless of its subject \u003ctt\u003ecommonName\u003c/tt\u003e.\u003c/p\u003e\u003cp\u003eSecond, \u003ctt\u003epublic_key:pkix_verify_hostname/3\u003c/tt\u003e in \u003ctt\u003elib/public_key/src/public_key.erl\u003c/tt\u003e falls back to the subject \u003ctt\u003ecommonName\u003c/tt\u003e when no \u003ctt\u003esubjectAltName\u003c/tt\u003e is present, extracting \u003ctt\u003eid-at-commonName\u003c/tt\u003e attributes as presented IDs and matching them against the reference hostname. The strict \u003ctt\u003epkix_verify_hostname_match_fun(https)\u003c/tt\u003e matcher does not suppress this fallback.\u003c/p\u003e\u003cp\u003eThe result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the \u003ctt\u003enameConstraints\u003c/tt\u003e are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock \u003ctt\u003essl:connect\u003c/tt\u003e with \u003ctt\u003everify_peer\u003c/tt\u003e, a trusted CA, SNI, and the canonical strict \u003ctt\u003ehttps\u003c/tt\u003e hostname matcher.\u003c/p\u003e\u003cp\u003eThis issue affects OTP from OTP 19.3 before OTP 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to \u003ctt\u003epublic_key\u003c/tt\u003e from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-295\", \"description\": \"CWE-295 Improper Certificate Validation\"}, {\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-297\", \"description\": \"CWE-297 Improper Validation of Certificate with Host Mismatch\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"26.2.5.21\", \"versionStartIncluding\": \"19.3\"}, {\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"27.3.4.12\", \"versionStartIncluding\": \"27.0\"}, {\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"28.5.0.1\", \"versionStartIncluding\": \"28.0\"}, {\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"29.0.1\", \"versionStartIncluding\": \"29.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-07-01T04:45:27.626Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-42790\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-01T04:45:27.626Z\", \"dateReserved\": \"2026-04-29T18:06:33.251Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-05-27T15:09:01.860Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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