CVE-2026-42789 (GCVE-0-2026-42789)
Vulnerability from cvelistv5 – Published: 2026-05-27 12:23 – Updated: 2026-05-27 15:46
VLAI
Title
Non-CA certificate accepted as intermediate issuer in public_key path validation
Summary
Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery.
In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement.
Any party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can use that certificate's private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers.
This issue affects OTP from OTP 17.0 before OTP 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 0.22 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.
Severity
CWE
Assigner
References
6 references
| URL | Tags |
|---|---|
| https://github.com/erlang/otp/security/advisories… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-42789.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-42789 | related |
| https://www.erlang.org/doc/system/versions.html#o… | x_version-scheme |
| https://github.com/erlang/otp/commit/471cd2f66430… | patch |
| https://github.com/erlang/otp/commit/59c8d824386b… | patch |
Impacted products
Credits
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[\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-42789\", \"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/471cd2f664300a95353c467873800bbe706005db\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd\", \"tags\": [\"patch\"]}], \"workarounds\": [{\"lang\": \"en\", \"value\": \"The verify_fun option in the ssl or public_key application can be used to ensure that path validation rejects chains where an intermediate certificate does not have basicConstraints cA:true.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"The \u003ctt\u003everify_fun\u003c/tt\u003e option in the \u003ctt\u003essl\u003c/tt\u003e or \u003ctt\u003epublic_key\u003c/tt\u003e application can be used to ensure that path validation rejects chains where an intermediate certificate does not have \u003ctt\u003ebasicConstraints cA:true\u003c/tt\u003e.\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Improper Following of a Certificate\u0027s Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery.\\n\\nIn lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement.\\n\\nAny party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim\u0027s trust store, can use that certificate\u0027s private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers.\\n\\nThis issue affects OTP from OTP 17.0 before OTP 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 0.22 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Improper Following of a Certificate\u0027s Chain of Trust vulnerability in Erlang OTP \u003ctt\u003epublic_key\u003c/tt\u003e (\u003ctt\u003epubkey_cert\u003c/tt\u003e module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery.\u003cp\u003eIn \u003ctt\u003elib/public_key/src/pubkey_cert.erl\u003c/tt\u003e, \u003ctt\u003epubkey_cert:validate_extensions/7\u003c/tt\u003e contains two flaws that together allow a certificate with \u003ctt\u003ebasicConstraints cA:false\u003c/tt\u003e and no \u003ctt\u003ekeyUsage\u003c/tt\u003e extension to be used as an intermediate issuer in a chain passed to \u003ctt\u003epublic_key:pkix_path_validation/3\u003c/tt\u003e: the \u003ctt\u003ecA:false\u003c/tt\u003e clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the \u003ctt\u003ekeyUsage\u003c/tt\u003e check only fires when the extension is present, so a certificate lacking \u003ctt\u003ekeyUsage\u003c/tt\u003e entirely bypasses the \u003ctt\u003ekeyCertSign\u003c/tt\u003e enforcement.\u003c/p\u003e\u003cp\u003eAny party holding an end-entity certificate with \u003ctt\u003ebasicConstraints cA:false\u003c/tt\u003e and no \u003ctt\u003ekeyUsage\u003c/tt\u003e extension, issued by any CA in the victim\u0027s trust store, can use that certificate\u0027s private key to sign forged leaf certificates for arbitrary identities. \u003ctt\u003epublic_key:pkix_path_validation/3\u003c/tt\u003e accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP \u003ctt\u003essl\u003c/tt\u003e application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers.\u003c/p\u003e\u003cp\u003eThis issue affects OTP from OTP 17.0 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 0.22 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-296\", \"description\": \"CWE-296 Improper Following of a Certificate\u0027s Chain of Trust\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"26.2.5.21\", \"versionStartIncluding\": \"17.0\"}, {\"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\": \"2026-05-27T15:46:57.832Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-42789\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-05-27T15:46:57.832Z\", \"dateReserved\": \"2026-04-29T18:06:33.251Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-05-27T12:23:06.355Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
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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