CVE-2024-56128

What it actually does

Apache Kafka's SCRAM implementation omits server-side nonce verification in the final authentication message as required by RFC 5802, allowing an intercepted plaintext exchange to complete without matching the server-issued nonce.

Why it matters to the business

Organizations using SCRAM authentication without TLS encryption face potential unauthorized access to Kafka clusters, which can lead to data exposure, message tampering, or cluster disruption; the low EPSS and absence from KEV indicate limited observed exploitation but require prompt attention for any plaintext deployments.

How an attack unfolds

An attacker positioned to observe unencrypted network traffic captures a SCRAM authentication exchange, crafts a client response that omits or mismatches the expected nonce, and completes authentication as a legitimate user without possessing valid credentials.

How to fix it

Upgrade Apache Kafka to version 3.7.2, 3.8.1, or 3.9.0; if upgrade is delayed, enforce TLS on all listeners and replace SASL_PLAINTEXT with SASL_SSL, or migrate to alternative mechanisms such as Kerberos or OAuth with TLS.

How to confirm the fix worked

Review server.properties for any SASL_PLAINTEXT listener entries; after upgrade confirm the presence of nonce verification logic in the SCRAM exchange and test authentication over both plaintext and TLS paths.

Typical attack path

1. Locate Kafka listeners configured with SASL_PLAINTEXT and SCRAM
2. Intercept the initial server nonce and subsequent client messages
3. Submit a manipulated final client message that bypasses nonce matching
4. Obtain an authenticated session to the broker

How to detect it

Search broker and client logs for SASL_PLAINTEXT listener configurations and any authentication events occurring on non-TLS ports; review network captures for SCRAM exchanges lacking TLS protection.

• SASL_PLAINTEXT
• listeners=.*SASL_PLAINTEXT

What your security team should do

• Immediately audit all Kafka clusters for SASL_PLAINTEXT usage and migrate to TLS-protected listeners
• Schedule upgrades to 3.7.2 or newer within the next maintenance window
• Add configuration scanning to CI/CD pipelines to block future plaintext SASL deployments