---
id: "CVE-2026-111115"
kind: "vulnerability"
aliases: ["CVE-2026-111115"]
title: "Apache Kafka: crafted request header forces memory exhaustion and broker denial of service"
severity: "high"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["broker", "kafka", "package", "self-hosted"]
not_affected_if: ["default-config"]
published_at: "2026-10-28T17:17:38+00:00"
first_seen_at: "2026-10-28T17:34:08+00:00"
updated_at: "2026-10-28T17:35:10+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-111115", "first_seen_at": "2026-10-28T17:34:08+00:00"}]
---

# Apache Kafka: crafted request header forces memory exhaustion and broker denial of service

Kafka's generated readers for flexible protocol versions trust a tagged-field count declared by the sender and allocate one object per declared field, with no bound beyond the request frame size. A client can send a request of a few tens of megabytes declaring about 20 million tagged fields, exhausting broker heap or stalling garbage collection before authentication.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `kafka-topics.sh --version` or check the Kafka build version on each broker and compare it with the fixed releases
- Check whether `socket.request.max.bytes` is set in `server.properties`, which only partly reduces exposure
- Check whether broker listeners are reachable from untrusted networks

## Fix

- Upgrade Apache Kafka to `4.2.2`, `4.3.2`, or `4.4.0`
- Until upgrading, lower `socket.request.max.bytes` and restrict network access to broker listeners (this reduces but does not remove exposure)

## Timeline

- 2026-10-28T17:34:08+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-111115

## From the sources

Apache Kafka's code-generated readers for flexible protocol versions read a tagged-field count declared by the sender and retain a RawTaggedField object for each unknown field. That count was bounded only by the outer request frame size (socket.request.max.bytes); it was not checked against the remaining buffer bytes or capped. Because each entry can be encoded in as little as two bytes (unknown tag 0, size 0), a modest request can declare tens of millions of tagged fields and force one object allocation per declared field. Flexible request headers (header version 2, used by flexible APIs such as ApiVersions v3) are parsed this way, so the amplification applies to the request header itself.


Impact:
The flexible request header is parsed on the network thread before authorization, request dispatch, and request-time quota accounting. A client can send a request of a few tens of megabytes whose header declares about 20 million tagged fields, forcing roughly that many RawTaggedField allocations and exhausting broker heap or inducing process-wide GC stalls, denying broker service. Because the header is parsed for pre-authentication APIs such as ApiVersions (v3), the allocation can occur before authentication; no Kafka resource ACL or quota is required.

Mitigation:
Upgrade to Apache Kafka 4.2.2, 4.3.2, or 4.4.0. Until then, lowering socket.request.max.bytes and restricting network access to broker listeners reduces, but does not remove, exposure.

Resolution:
From Apache Kafka 4.2.2, 4.3.2, and 4.4.0: generated readers bounds-check the tagged-field count for flexible-versioned messages, rejecting a negative count, a count exceeding the remaining buffer bytes, or a count exceeding a fixed maximum (10,000), before any per-field allocation.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_