Bug 2489979 (CVE-2026-9675)

Summary:	CVE-2026-9675 undici: undici WebSocket client vulnerable to denial of service via cumulative fragment bypass
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	aazores, abarbaro, alizardo, ataylor, cdrage, cmah, dbruscin, dschmidt, eaguilar, ebaron, ehugonne, erezende, gbenhaim, jchui, jhe, jkoehler, jlanda, jmatsuok, jolong, jtolenti, kaycoth, kshier, ktsao, kvanderr, lphiri, manissin, nboldt, niyer, oaljalju, pjindal, psrna, rhel-process-autobot, rushinde, sdawley, simaishi, smcdonal, stcannon, teagle, twaugh, watson-tool-maintainers, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in undici. A malicious WebSocket server could exploit this vulnerability by sending fragmented messages that individually meet size limits but collectively exceed them. This can lead to unbounded memory growth in the client process, resulting in memory exhaustion and a denial of service (DoS).	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-06-17 17:02:05 UTC

Impact:
The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.

Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.

This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.

Patches:
Upgrade to undici >= 8.5.0.

Workarounds:
No workaround is available. The fix must be applied through an upgrade.