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


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-fpf4-qx46-w5rg, UBUNTU-CVE-2026-111551

## What is CVE-2026-111551?

CVE-2026-111551 is a vulnerability in Apache Kafka, published on 28 Oct 2026. 

### Official 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.

Weakness: CWE-789 (Memory Allocation with Excessive Size Value), CWE-400 (Uncontrolled Resource Consumption), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-111551?


## How do I fix CVE-2026-111551?

No fix has been published for CVE-2026-111551 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-111551 being exploited?

There is no known exploitation of CVE-2026-111551 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-111551 and fix it if it is affected.

What it is: CVE-2026-111551 is a vulnerability in Apache Kafka, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-111551 in the wild and no public exploit code.

Affected product: Apache Kafka. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-111551/ (Markdown: https://insights.sbomify.com/CVE-2026-111551/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-111551
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-111551
- OSV: https://osv.dev/vulnerability/CVE-2026-111551

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-111551/
Summaries are generated and may contain mistakes; the official description above is the record.