CVE-2021-3527: security - CVE-2021-3527 QEMU: usb: unbounded stack allocation in usbredir

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Date: Wed, 5 May 2021 19:09:40 +0200 From: Mauro Matteo Cascella <mcascell@…hat.com> To: oss-security@…ts.openwall.com Cc: Remy Noel <remy.noel@…de-group.com> Subject: CVE-2021-3527 QEMU: usb: unbounded stack allocation in usbredir

Hello,

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 usb/mtp).

Upstream patchset: https://lists.nongnu.org/archive/html/qemu-devel/2021-05/msg00564.html

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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