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GHSA-R6JR-F97R-9CC7

Vulnerability from github – Published: 2026-10-28 18:32 – Updated: 2026-10-28 18:32

Details

The issuer (iss) claim is verified only when sasl.oauthbearer.expected.issuer is set. When it is unset, a validly-signed token carrying the expected audience is accepted regardless of which issuer minted it.
An audience (aud) claim is required only when sasl.oauthbearer.expected.audience is set. When it is unset, a validly-signed token that omits the aud claim is accepted. (A token that carries an aud claim is still rejected when no expected audience is configured.)

Both options default to unset and have been documented as optional (Importance LOW) since KIP-768 (3.1.0).

Impact: The exposure is realizable mainly in deployments whose JWKS endpoint serves signing keys for more than one issuer (a multi-tenant identity provider, an aggregated/shared JWKS, or shared signing keys): a token minted for a different issuer, or a token lacking an audience, may be accepted to authenticate — potentially as a higher-privileged principal. In a single-issuer deployment where the provider controls the iss claim and issues audience-scoped tokens, exposure is limited. The signature trust anchor remains enforced in all cases. This is distinct from CVE-2026-33557 (acceptance of unsigned/unvalidated tokens); here the signature is validated and only the issuer/audience checks are not enforced by default.

Mitigation (all affected versions, no upgrade required): Set both sasl.oauthbearer.expected.issuer (to your provider's exact iss value) and sasl.oauthbearer.expected.audience (to the audience(s) your brokers expect), per listener. Brokers that set these perform exact-match issuer/audience checks and are not affected. Both have been available since 3.1.0.

Resolution: - From Apache Kafka 4.4.0: a broker configured with a JWKS endpoint fails to start unless both sasl.oauthbearer.expected.issuer and sasl.oauthbearer.expected.audience are set (secure by default). Deployments that intentionally do not restrict the issuer and/or audience may opt out per axis with sasl.oauthbearer.allow.unverified.issuer=true and/or sasl.oauthbearer.allow.unverified.audience=true.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-110952"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-345"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-28T17:17:37Z",
    "severity": null
  },
  "details": "A Kafka broker that authenticates clients with SASL/OAUTHBEARER using the bundled JWKS-backed validator always verifies the JWT signature, but two further checks are only performed when explicitly configured:\n\n- The issuer (iss) claim is verified only when sasl.oauthbearer.expected.issuer is set. When it is unset, a validly-signed token carrying the expected audience is accepted regardless of which issuer minted it.\n- An audience (aud) claim is required only when sasl.oauthbearer.expected.audience is set. When it is unset, a validly-signed token that omits the aud claim is accepted. (A token that carries an aud claim is\n  still rejected when no expected audience is configured.)\n\nBoth options default to unset and have been documented as optional (Importance LOW) since KIP-768 (3.1.0).\n\nImpact:\n  The exposure is realizable mainly in deployments whose JWKS endpoint serves signing keys for more than one issuer (a multi-tenant identity provider, an aggregated/shared JWKS, or shared signing keys): a token\n  minted for a different issuer, or a token lacking an audience, may be accepted to authenticate \u2014 potentially as a higher-privileged principal. In a single-issuer deployment where the provider controls the iss\n  claim and issues audience-scoped tokens, exposure is limited. The signature trust anchor remains enforced in all cases. This is distinct from CVE-2026-33557 (acceptance of unsigned/unvalidated tokens); here the\n  signature is validated and only the issuer/audience checks are not enforced by default.\n\nMitigation (all affected versions, no upgrade required):\n  Set both sasl.oauthbearer.expected.issuer (to your provider\u0027s exact iss value) and sasl.oauthbearer.expected.audience (to the audience(s) your brokers expect), per listener. Brokers that set these perform\n  exact-match issuer/audience checks and are not affected. Both have been available since 3.1.0.\n\nResolution:\n  - From Apache Kafka 4.4.0: a broker configured with a JWKS endpoint fails to start unless both sasl.oauthbearer.expected.issuer and sasl.oauthbearer.expected.audience are set (secure by default). Deployments that\n  intentionally do not restrict the issuer and/or audience may opt out per axis with sasl.oauthbearer.allow.unverified.issuer=true and/or sasl.oauthbearer.allow.unverified.audience=true.",
  "id": "GHSA-r6jr-f97r-9cc7",
  "modified": "2026-10-28T18:32:03Z",
  "published": "2026-10-28T18:32:03Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110952"
    },
    {
      "type": "WEB",
      "url": "https://kafka.apache.org/cve-list"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-110952 (GCVE-0-2026-110952)

Vulnerability from cvelistv5 – Published: 2026-10-28 16:37 – Updated: 2026-10-28 16:37

Title

Apache Kafka: Broker does not enforce JWT issuer and audience validation for SASL/OAUTHBEARER by default

Summary

A Kafka broker that authenticates clients with SASL/OAUTHBEARER using the bundled JWKS-backed validator always verifies the JWT signature, but two further checks are only performed when explicitly configured: - The issuer (iss) claim is verified only when sasl.oauthbearer.expected.issuer is set. When it is unset, a validly-signed token carrying the expected audience is accepted regardless of which issuer minted it. - An audience (aud) claim is required only when sasl.oauthbearer.expected.audience is set. When it is unset, a validly-signed token that omits the aud claim is accepted. (A token that carries an aud claim is still rejected when no expected audience is configured.) Both options default to unset and have been documented as optional (Importance LOW) since KIP-768 (3.1.0). Impact: The exposure is realizable mainly in deployments whose JWKS endpoint serves signing keys for more than one issuer (a multi-tenant identity provider, an aggregated/shared JWKS, or shared signing keys): a token minted for a different issuer, or a token lacking an audience, may be accepted to authenticate — potentially as a higher-privileged principal. In a single-issuer deployment where the provider controls the iss claim and issues audience-scoped tokens, exposure is limited. The signature trust anchor remains enforced in all cases. This is distinct from CVE-2026-33557 (acceptance of unsigned/unvalidated tokens); here the signature is validated and only the issuer/audience checks are not enforced by default. Mitigation (all affected versions, no upgrade required): Set both sasl.oauthbearer.expected.issuer (to your provider's exact iss value) and sasl.oauthbearer.expected.audience (to the audience(s) your brokers expect), per listener. Brokers that set these perform exact-match issuer/audience checks and are not affected. Both have been available since 3.1.0. Resolution: - From Apache Kafka 4.4.0: a broker configured with a JWKS endpoint fails to start unless both sasl.oauthbearer.expected.issuer and sasl.oauthbearer.expected.audience are set (secure by default). Deployments that intentionally do not restrict the issuer and/or audience may opt out per axis with sasl.oauthbearer.allow.unverified.issuer=true and/or sasl.oauthbearer.allow.unverified.audience=true.

Severity

No CVSS data available.

CWE

CWE-345 - Insufficient Verification of Data Authenticity)
CWE-1188 - Initialization of a resource with an insecure default

Assigner

apache CNA under the mitre root

CNA scorecard B 76/100 over 1090 records in the last 180 days details

References

1 reference

URL	Tags
https://kafka.apache.org/cve-list	vendor-advisory

Impacted products

1 product

Vendor	Product	Version
Apache Software Foundation	Apache Kafka	Affected: 3.1.0 , < 4.4.0 (semver)

Credits

Kai Aizen <kai.aizen.dev@gmail.com>, SnailSploit Evan Zhou <ezhou@confluent.io>

Show details on NVD website

JSON

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Sightings

Author	Source	Type	Date	Other

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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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