Bug 2537961

Summary:	CVE-2026-93834 qemu: 9pfs: use-after-free race in Tlcreate/Twalk allows VM guest escape [fedora-all]
Product:	[Fedora] Fedora	Reporter:	Mauro Matteo Cascella <mcascell>
Component:	qemu	Assignee:	Fedora Virtualization Maintainers <virt-maint>
Status:	NEW ---	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	high	Docs Contact:
Priority:	high
Version:	rawhide	CC:	berrange, cfergeau, crobinso, mcascell, pbonzini, rjones, suraj.ghimire7, virt-maint
Target Milestone:	---	Keywords:	Security, SecurityTracking
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:	{"flaws": ["e93973c1-0a8a-468a-a5f6-31ab0587824f"]}
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Regression:	---	Mount Type:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	2537939

Description Mauro Matteo Cascella 2026-09-22 16:21:39 UTC

Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A use-after-free race condition was found in QEMU's 9pfs (virtfs) subsystem. When processing a Tlcreate request, v9fs_co_open2() frees and replaces fidp->path on a worker thread. If a concurrent Twalk on the main thread reads the old path length before the free and copies bytes after the memory is reused, the resulting fid path contains stale heap data that bypasses the share directory boundary. A malicious guest user with access to a 9P mount can exploit this to read/write arbitrary host files and execute commands as the QEMU process user, achieving a VM escape. The regression was introduced in QEMU v6.1.0 by commit 8d6cb100731c.