CVE-2026-112375: Apache Kafka: Unauthorized principal can read arbitrary broker files via IncrementalAlterConfigs
An authenticated Kafka principal with no authorization grants (not even ALTERCONFIGS) can make a broker read a file or an environment variable from the broker host and return its contents. An IncrementalAlterConfigs (or AlterConfigs) request targeting a BROKER resource reaches the broker's configuration validation before any authorization check is applied to that path. Validation resolves configuration variables such as ${file:/path:key} or ${env:VAR} using a ConfigProvider named in the request, and this resolution bypasses the org.apache.kafka.automatic.config.providers allowlist that was added as the mitigation for CVE-2024-31141. An arbitrary ConfigProvider (for example FileConfigProvider or EnvVarConfigProvider) is therefore instantiated and the referenced file or environment variable is read, and a type-validation error returns the resolved content to the caller.
Impact:
On a cluster with an authorizer enabled, an authenticated principal with no authorization grants can read the contents of files accessible to the broker process, and the broker's environment variables, exposing credentials, keystores, or other secrets, defeating the CVE-2024-31141 allowlist. The read is bounded by the broker process's file permissions. The brokers and the cluster remain available; the issue is disclosure of file and environment- variable contents. Clusters with no authorizer configured are not affected in practice, because every principal already holds ALTERCONFIGS there.
Mitigation:
Upgrade to Apache Kafka 4.2.2, 4.3.2, or 4.4.0. As defense in depth, run brokers under a least-privileged operating-system account so that sensitive files are not readable by the broker process.
Resolution:
From Apache Kafka 4.2.2, 4.3.2, and 4.4.0: broker configuration changes are authorized (ALTERCONFIGS on the cluster) before the configuration is validated, and configuration- variable resolution enforces the config-providers allowlist.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Apache Kafkato a version that resolves this vulnerability.Fixed in 4.4.0 - Compensating control
Run Kafka brokers under a least-privileged operating-system account so sensitive files are not readable by the broker process.
Event History
Frequently Asked Questions
Does enabling an authorizer or withholding ALTER_CONFIGS permission prevent exploitation?
No. An authenticated principal with no authorization grants, including no ALTER_CONFIGS grant, can reach broker configuration validation before authorization is checked for this request path.
What access does an attacker need?
The attacker needs an authenticated Kafka principal and the ability to send an IncrementalAlterConfigs or AlterConfigs request targeting a BROKER resource. No configuration-alter authorization is required according to the provided information.
Can the automatic ConfigProvider allowlist mitigate this issue?
No. The validation path bypasses the org.apache.kafka.automatic.config.providers allowlist. A ConfigProvider named in the request can be instantiated, including file and environment-variable providers.
What data may be exposed from an affected broker?
An attacker may read files accessible to the broker process and environment variables from the broker host. This can expose credentials, keystores, and other secrets, with resolved values returned through a type-validation error.