Bug 2537958 - CVE-2026-93834 unicorn: 9pfs: use-after-free race in Tlcreate/Twalk allows VM guest escape [fedora-all]
Summary: CVE-2026-93834 unicorn: 9pfs: use-after-free race in Tlcreate/Twalk allows VM...
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Fedora
Classification: Fedora
Component: unicorn
Version: rawhide
Hardware: Unspecified
OS: Unspecified
high
high
Target Milestone: ---
Assignee: W. Michael Petullo
QA Contact: Fedora Extras Quality Assurance
URL:
Whiteboard: {"flaws": ["e93973c1-0a8a-468a-a5f6-3...
Depends On:
Blocks: CVE-2026-93834
TreeView+ depends on / blocked
 
Reported: 2026-09-22 16:21 UTC by Mauro Matteo Cascella
Modified: 2026-09-22 16:24 UTC (History)
2 users (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed: 2026-09-22 16:24:43 UTC
Type: ---
Embargoed:


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Description Mauro Matteo Cascella 2026-09-22 16:21:31 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.

Comment 1 Mauro Matteo Cascella 2026-09-22 16:24:43 UTC
Unicorn ships qemu-2.2.1. This CVE was introduced via commit 8d6cb100731c [1] from v6.1.0+

[1] https://gitlab.com/qemu-project/qemu/-/commit/8d6cb100731c4d28535adbf2a3c2d1f29be3fef4


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