cve-2026-42789

{
  "cvss": 7.0,
  "datePublished": "2026-05-27T14:16:53.267",
  "dateUpdated": "2026-09-18T13:18:22.333",
  "description": "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.\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'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.\n\nThis issue affects OTP from OTP 17.0 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 0.22 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.",
  "id": "CVE-2026-42789",
  "raw": {
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      {
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              "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
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            "defaultStatus": "unknown",
            "modules": [
              "pubkey_cert"
            ],
            "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"
            ],
            "programRoutines": [
              {
                "name": "pubkey_cert:validate_extensions/7"
              }
            ],
            "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": "0.22",
                "versionType": "otp"
              }
            ]
          },
          {
            "collectionURL": "https://github.com",
            "cpes": [
              "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
            ],
            "defaultStatus": "unknown",
            "modules": [
              "pubkey_cert"
            ],
            "packageName": "erlang/otp",
            "packageURL": "pkg:github/erlang/otp",
            "product": "OTP",
            "programFiles": [
              "lib/public_key/src/pubkey_cert.erl"
            ],
            "programRoutines": [
              {
                "name": "pubkey_cert:validate_extensions/7"
              }
            ],
            "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": "17.0",
                "versionType": "otp"
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                    "at": "471cd2f664300a95353c467873800bbe706005db",
                    "status": "unaffected"
                  },
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                    "at": "59c8d824386b2eb1614ff9340624843ef6aca0fd",
                    "status": "unaffected"
                  }
                ],
                "lessThan": "*",
                "status": "affected",
                "version": "84adefa331c4159d432d22840663c38f155cd4c1",
                "versionType": "git"
              }
            ]
          }
        ],
        "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
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              "cpe:/a:redhat:openstack:16.2::el8"
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            "defaultStatus": "affected",
            "packageName": "erlang",
            "product": "Red Hat OpenStack Platform 16.2",
            "vendor": "Red Hat",
            "versions": [
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                "status": "unaffected",
                "version": "0:23.3.4.18-2.el8ost",
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            "product": "Red Hat OpenStack Services on OpenShift 18.0",
            "vendor": "Red Hat",
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                "status": "unaffected",
                "version": "0:26.2.5.21-2.el9ost",
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            "cpes": [
              "cpe:/a:redhat:hummingbird:1"
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            "defaultStatus": "affected",
            "packageName": "erlang27",
            "product": "Red Hat Hardened Images",
            "vendor": "Red Hat"
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          {
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            "cpes": [
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            "packageName": "erlang",
            "product": "Red Hat OpenStack Platform 17.1",
            "vendor": "Red Hat"
          }
        ],
        "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c"
      }
    ],
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                "criteria": "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*",
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                "versionEndExcluding": "26.2.5.21",
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            "negate": false,
            "operator": "OR"
          }
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    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "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.\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'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.\n\nThis issue affects OTP from OTP 17.0 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 0.22 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7."
      }
    ],
    "id": "CVE-2026-42789",
    "lastModified": "2026-09-18T13:18:22.333",
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            "baseScore": 4.8,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
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            "baseScore": 8.0,
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            "confidentialityImpact": "HIGH",
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            "userInteraction": "REQUIRED",
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            "Recovery": "NOT_DEFINED",
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            "availabilityRequirement": "NOT_DEFINED",
            "baseScore": 7.0,
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            "confidentialityRequirement": "NOT_DEFINED",
            "exploitMaturity": "NOT_DEFINED",
            "integrityRequirement": "NOT_DEFINED",
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            "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",
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            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
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            "role": "CISA Coordinator",
            "timestamp": "2026-05-27T15:41:47.903975Z",
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    "vulnStatus": "Modified",
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        "description": [
          {
            "lang": "en",
            "value": "CWE-295"
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            "lang": "en",
            "value": "CWE-296"
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  },
  "severity": "HIGH",
  "source": "nvd",
  "title": "Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allo..."
}