Apache Kafka: Broker OutOfMemoryError via tagged-field allocation amplification in flexible protocol request parsing

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-111115
StatePUBLISHED
Assignerapache
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-28 17:17:38 UTC
Updated2026-10-28 20:17:17 UTC
DescriptionApache 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Apache Software Foundation Apache Kafka affected 2.4.0 4.1.2 semver Not specified
CNA Apache Software Foundation Apache Kafka affected 4.2.0 4.2.1 semver Not specified
CNA Apache Software Foundation Apache Kafka affected 4.3.0 4.3.1 semver Not specified

References

ReferenceSourceLinkTags
kafka.apache.org/cve-list [email protected] kafka.apache.org
www.openwall.com/lists/oss-security/2026/10/28/12 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Mufeed VH <[email protected]> (en)

CNA: Vivek R <[email protected]> (en)

CNA: Shay Elkin <[email protected]> (en)

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