CVE-2026-110985
Received
Received - Intake
JWT Signature Bypass in Apache Kafka
Vulnerability report for CVE-2026-110985, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-28
Last updated on: 2026-10-28
Assigner: Apache Software Foundation
Description
Description
A Kafka broker using SASL/OAUTHBEARER with the default validator (sasl.oauthbearer.jwt.validator.class=DefaultJwtValidator) selects its implementation from configuration. When sasl.oauthbearer.jwks.endpoint.url is set, the validator verifies the JWT signature. When that URL is unset (the default) and no verification key resolver is supplied, DefaultJwtValidator silently falls back to ClientJwtValidator, which does not verify the JWT signature, algorithm, or issuer - and the broker starts with no warning or error. This is the residual of CVE-2026-33557, whose fix restored signature verification only on the path where the JWKS endpoint URL is set.
Impact:
A broker in this state accepts any structurally valid JWT, including "alg":"none" tokens. An unauthenticated remote attacker who can reach the listener can forge a token asserting any principal - including configured superusers - and gain full access to the cluster. Only brokers that enable SASL/OAUTHBEARER validation without a JWKS endpoint URL (and without a custom verification key resolver) are affected; brokers that set the URL verify signatures and are not affected. Unlike CVE-2026-110952 (issuer/audience not enforced by default), here no signature is verified at all.
Mitigation (all affected versions, no upgrade required):
Set sasl.oauthbearer.jwks.endpoint.url for every listener/mechanism that uses OAuthBearerValidatorCallbackHandler, or configure a signature-verifying sasl.oauthbearer.jwt.validator.class.
Resolution:
From Apache Kafka 4.2.2, 4.3.1, and 4.4.0: a broker that would fall back to the non-verifying ClientJwtValidator fails to start with a ConfigException instead of running without signature verification (secure by default).
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| Apache Software Foundation | Apache Kafka | 4.1.0 |
| Apache Software Foundation | Apache Kafka | 4.2.0 |
| Apache Software Foundation | Apache Kafka | 4.3.0 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-347 | The product does not verify, or incorrectly verifies, the cryptographic signature for data. |
| CWE-636 | When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions. |
| CWE-345 | The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. |
| CWE-1287 | The product receives input that is expected to be of a certain type, but it does not validate or incorrectly validates that the input is actually of the expected type. |
