CVE-2026-35554

A race condition in the Apache Kafka Java producer client’s buffer pool management can cause messages to be silently delivered to incorrect topics.

When a produce batch expires due to delivery.timeout.ms while a network request containing that batch is still in flight, the batch’s ByteBuffer is prematurely deallocated and returned to the buffer pool. If a subsequent producer batch, potentially destined for a different topic, reuses this freed buffer before the original network request completes, the buffer contents may become corrupted. This can result in messages being delivered to unintended topics without any error being reported to the producer.

Data Confidentiality:
Messages intended for one topic may be delivered to a different topic, potentially exposing sensitive data to consumers who have access to the destination topic but not the intended source topic.

Data Integrity:
Consumers on the receiving topic may encounter unexpected or incompatible messages, leading to deserialization failures, processing errors, and corrupted downstream data.

This issue affects Apache Kafka versions ≤ 3.9.1, ≤ 4.0.1, and  ≤ 4.1.1.

Kafka users are advised to upgrade to 3.9.2, 4.0.2, 4.1.2, 4.2.0, or later to address this vulnerability.

Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.

CVE-2026-35554 has a CVSS score of 8.7 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.9.2, 4.0.2, 4.1.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-35554? CVE-2026-35554 is a high-severity race condition vulnerability in org.apache.kafka:kafka-clients (maven), affecting versions >= 2.8.0, < 3.9.2. It is fixed in 3.9.2, 4.0.2, 4.1.2. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
2. How severe is CVE-2026-35554? CVE-2026-35554 has a CVSS score of 8.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of org.apache.kafka:kafka-clients are affected by CVE-2026-35554? org.apache.kafka:kafka-clients (maven) versions >= 2.8.0, < 3.9.2 is affected.
4. Is there a fix for CVE-2026-35554? Yes. CVE-2026-35554 is fixed in 3.9.2, 4.0.2, 4.1.2. Upgrade to this version or later.
5. Is CVE-2026-35554 exploitable, and should I be worried? Whether CVE-2026-35554 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-35554 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-35554?
   • Upgrade org.apache.kafka:kafka-clients to 3.9.2 or later
   • Upgrade org.apache.kafka:kafka-clients to 4.0.2 or later
   • Upgrade org.apache.kafka:kafka-clients to 4.1.2 or later