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Date: Wed, 5 May 2021 19:09:40 +0200
From: Mauro Matteo Cascella <>
Cc: Remy Noel <>
Subject: CVE-2021-3527 QEMU: usb: unbounded stack allocation in usbredir


A flaw was found in the USB redirector device (usb-redir) of QEMU.
Small USB packets are combined into a single, large transfer request,
to reduce the overhead and improve performance. The combined size of
the bulk transfer is used to dynamically allocate a variable length
array (VLA) on the stack without proper validation. Since the total
size is not bounded, a malicious guest could use this flaw to
influence the array length and cause the QEMU process to perform an
excessive allocation on the stack, resulting in a denial of service.

Note: in addition to usb-redir, the patchset below fixes other places
in the code where stack-allocated VLAs were used (notably, usb/hid and

Upstream patchset:

Acknowledgements: Remy Noel (cc'd).
CVE-2021-3527 assigned by Red Hat, Inc.

Best regards.
Mauro Matteo Cascella
Red Hat Product Security
PGP-Key ID: BB3410B0

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