A flaw was found in qemu Media Transfer Protocol (MTP). The code opening files
in usb_mtp_get_object and usb_mtp_get_partial_object and directories in
usb_mtp_object_readdir doesn't consider that the underlying filesystem may have
changed since the time lstat(2) was called in usb_mtp_object_alloc, a classical
TOCTTOU problem. An attacker with write access to the host filesystem shared with
a guest can use this property to navigate the host filesystem in the context of
the QEMU process and read any file the QEMU process has access to. Access to the
filesystem may be local or via a network share protocol such as CIFS.

Upstream patch:
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  -> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg03135.html

Reference:
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  -> https://www.openwall.com/lists/oss-security/2018/12/13/11