Bug 2562997 (CVE-2026-111115)

Summary:	CVE-2026-111115 org.apache.kafka/kafka-clients: Apache Kafka: Denial of Service via uncontrolled memory allocation in flexible request headers
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	ant, asyoung, ccranfor, cescoffi, chfoley, cmah, dhanak, drosa, dsimansk, ewittman, fmariani, fmongiar, gmalinko, gsmet, gtanzill, janstey, jbuscemi, jhollowa, jmartisk, jnethert, jpechane, jturenov, jwon, kaycoth, kingland, manderse, mcarlett, mnovotny, nipatil, olubyans, ozzy, pantinor, pdelbell, pjindal, prichard, rguimara, rhel-process-autobot, rkubis, rstepani, sausingh, sbiarozk, sthirugn, swoodman, tcunning, varjain, watson-tool-maintainers, yfang
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in Apache Kafka. An unauthenticated remote attacker can exploit this vulnerability by sending a specially crafted request containing a large declared count of tagged fields in flexible request headers. Because the server does not adequately validate or limit this count against the incoming data buffer, it allocates an excessive number of memory objects before authentication or quota checks occur. This can exhaust system memory, leading to broker unresponsiveness and a Denial of Service (DoS).	Story Points:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-28 17:16:35 UTC

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.