# CVE-2026-114349: Apache Kafka: Denial of service via unbounded memory allocation when decoding compressed record batches

Status: published. Published: 2026-10-28. Updated: 2026-11-05.

When a broker decodes a compressed record batch, the per-record decoder reads a declared body size from the decompressed stream and allocates a buffer of that size before validating it against the bytes available or any configured limit. The size is attacker-controlled, and the batch CRC does not constrain it, so a small (around 90-byte), CRC-valid compressed produce request can declare a body size of up to about 2 GiB and force the broker to attempt that allocation, raising OutOfMemoryError. The record size limit (max.message.bytes), the request size limit, and client/broker quotas bound only the compressed wire size, not the declared decompressed size.


Impact:

An authenticated principal with Write on a topic can crash broker request-handler threads (reached when a batch's codec differs from the topic's compression.type and records are re-encoded) and any consumer that fetches the record, denying service. On brokers started with -XX:+ExitOnOutOfMemoryError, a common hardening, a single crafted request terminates the broker JVM. More seriously, a crafted record  is accepted at ingest and written to disk; when the log-cleaner later reads it on a compacted topic, the OutOfMemoryError (an Error, not an Exception) terminates the cleaner thread, which is not restarted. With the default of a single cleaner thread, log compaction then stops for the entire broker, including the internal __consumer_offsets and __transaction_state topics, and the condition persists across restarts until the offending record is removed. The impact is availability only; no data is disclosed or altered.


Mitigation:

Upgrade to Apache Kafka 4.2.2, 4.3.2, or 4.4.0, and set max.decompressed.message.bytes (at the broker and/or topic level) to a bounded value appropriate for your workload. Upgrading alone is not sufficient: for backward compatibility this configuration defaults to an effectively unlimited value (about 2 GiB), so a broker remains exposed until the limit is set. Choose a value at or slightly above the largest legitimate decompressed record your applications produce, and comfortably below the broker heap divided by the number of request-handler and cleaner threads. Until you can upgrade and configure the limit, restrict Write access to trusted producers; quotas and max.message.bytes do not mitigate this issue.


Resolution:

From Apache Kafka 4.2.2, 4.3.2, and 4.4.0: the broker validates a record's declared decompressed body size against max.decompressed.message.bytes before allocating, on the produce-validation, log-compaction, and timestamp-lookup paths, and rejects oversized or negative sizes with InvalidRecordException. Operators must set this configuration to a bounded value to be protected, as its default is effectively unlimited.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Apache Software Foundation / Apache Kafka (org.apache.kafka:kafka_2.11): ≥ 0.11.0.0; < 2.5.0 (affected, maven). Source: CNA: apache
- Apache Software Foundation / Apache Kafka (org.apache.kafka:kafka_2.12): ≥ 0.11.0.0; < 4.0.0 (affected, maven). Source: CNA: apache
- Apache Software Foundation / Apache Kafka (org.apache.kafka:kafka_2.13): ≥ 2.4.0; ≤ 4.1.2 (affected, maven); ≥ 4.2.0; ≤ 4.2.1 (affected, maven); ≥ 4.3.0; ≤ 4.3.1 (affected, maven). Source: CNA: apache

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H; source: ADP: CISA-ADP

- CISA KEV: No listing in collected sources

- EPSS: 0.25% as of 2026-11-05; percentile 16.15%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-789, CWE-400, CWE-1284

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://kafka.apache.org/cve-list (CNA: apache; vendor-advisory)

- https://lists.apache.org/thread/hdy56hrd1h9btf30jb1noswsx32l17dq (CNA: apache; mailing-list)

- http://www.openwall.com/lists/oss-security/2026/10/28/18 (ADP: CVE)

## Provenance

- CNA: apache: https://www.cve.org/CVERecord?id=CVE-2026-114349; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-114349; retrieved 2026-11-05; source updated Not reported

Revision: 0664c84b5f4c5a8b3d2c54cb24ec61276214c1e74c2dfca471cbc325fb71488b

Canonical: https://y2.dev/cve/CVE-2026-114349

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