CVE-2026-111551 Apache Kafka: Denial of service in Kafka Streams and client deserializers via unbounded memory allocation
- Exploited in the wild
- Not known
- Fix
- None listed
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.
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.
Sources
Also known as GHSA-fpf4-qx46-w5rg, UBUNTU-CVE-2026-111551.