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Non-CA certificate accepted as intermediate issuer in public_key path validation

Type: advisorySource: Official CVE List1 source record

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 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to public_key from 0.22 before 1.17.1.7, 1.20.3.6, and 1.21.8. Whether OTP before OTP

Announced Source revision 1
Original source ↗

CVE-2026-42789

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-42789

OTP

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
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Prerequisites
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OTP

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

OTP

Source reference: /containers/cna/affected/2/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "cpes": [
      "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
    ],
    "vendor": "Erlang",
    "modules": [
      "pubkey_cert"
    ],
    "product": "OTP",
    "versions": [
      {
        "status": "affected",
        "changes": [
          {
            "at": "27.3.4.19",
            "status": "unaffected"
          },
          {
            "at": "28.5.0.8",
            "status": "unaffected"
          },
          {
            "at": "29.1.2",
            "status": "unaffected"
          }
        ],
        "version": "17.0",
        "lessThan": "*",
        "versionType": "otp"
      }
    ],
    "packageURL": "pkg:software-id/erlang.org/otp",
    "packageName": "otp",
    "programFiles": [
      "lib/public_key/src/pubkey_cert.erl"
    ],
    "defaultStatus": "unknown",
    "programRoutines": [
      {
        "name": "pubkey_cert:validate_extensions/7"
      }
    ]
  },
  {
    "cpes": [
      "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
    ],
    "repo": "https://github.com/erlang/otp",
    "vendor": "Erlang",
    "modules": [
      "pubkey_cert"
    ],
    "product": "OTP",
    "versions": [
      {
        "status": "affected",
        "changes": [
          {
            "at": "1.17.1.7",
            "status": "unaffected"
          },
          {
            "at": "1.20.3.6",
            "status": "unaffected"
          },
          {
            "at": "1.21.8",
            "status": "unaffected"
          }
        ],
        "version": "0.22",
        "lessThan": "*",
        "versionType": "otp"
      }
    ],
    "packageURL": "pkg:otp/public_key?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp&vcs_url=git%2Bhttps:%2F%2Fgithub.com%2Ferlang%2Fotp.git",
    "packageName": "public_key",
    "programFiles": [
      "src/pubkey_cert.erl"
    ],
    "defaultStatus": "unknown",
    "programRoutines": [
      {
        "name": "pubkey_cert:validate_extensions/7"
      }
    ]
  },
  {
    "cpes": [
      "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
    ],
    "repo": "https://github.com/erlang/otp",
    "vendor": "Erlang",
    "modules": [
      "pubkey_cert"
    ],
    "product": "OTP",
    "versions": [
      {
        "status": "affected",
        "changes": [
          {
            "at": "0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8",
            "status": "unaffected"
          },
          {
            "at": "75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333",
            "status": "unaffected"
          },
          {
            "at": "82af606b5437c4de1276dbcc8855a47e88231226",
            "status": "unaffected"
          }
        ],
        "version": "84adefa331c4159d432d22840663c38f155cd4c1",
        "lessThan": "*",
        "versionType": "git"
      },
      {
        "status": "unaffected",
        "version": "0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8",
        "lessThan": "*",
        "versionType": "git"
      },
      {
        "status": "unaffected",
        "version": "75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333",
        "lessThan": "*",
        "versionType": "git"
      },
      {
        "status": "unaffected",
        "version": "82af606b5437c4de1276dbcc8855a47e88231226",
        "lessThan": "*",
        "versionType": "git"
      }
    ],
    "packageURL": "pkg:github/erlang/otp",
    "packageName": "erlang/otp",
    "programFiles": [
      "lib/public_key/src/pubkey_cert.erl"
    ],
    "collectionURL": "https://github.com",
    "defaultStatus": "unknown",
    "programRoutines": [
      {
        "name": "pubkey_cert:validate_extensions/7"
      }
    ]
  }
]
Related CVEs
CVE-2026-42789

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#22797 · Revision 1
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Publisher date
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