Exploit the possiblities

QEMU 2.10 Buffer Overflow

QEMU 2.10 Buffer Overflow
Posted Nov 29, 2017
Authored by Eric Blake

QEMU version 2.10 suffers from an NBD server long export name stack buffer overflow vulnerability. This was introduced with commit f37708f6b8.

tags | exploit, overflow
advisories | CVE-2017-15118
MD5 | cd918a363b2e2a85e3195712b7c48c43

QEMU 2.10 Buffer Overflow

Change Mirror Download
Introduced in commit f37708f6b8 (2.10).  The NBD spec says a client
can request export names up to 4096 bytes in length, even though
they should not expect success on names longer than 256. However,
qemu hard-codes the limit of 256, and fails to filter out a client
that probes for a longer name; the result is a stack smash that can
potentially give an attacker arbitrary control over the qemu
process.

The smash can be easily demonstrated with this client:

$ qemu-io f raw nbd://localhost:10809/$(printf %3000d 1 | tr ' ' a)

If the qemu NBD server binary (whether the standalone qemu-nbd, or
the builtin server of QMP nbd-server-start) was compiled with
-fstack-protector-strong, the ability to exploit the stack smash
into arbitrary execution is a lot more difficult (but still
theoretically possible to a determined attacker, perhaps in
combination with other CVEs). Still, crashing a running qemu (and
losing the VM) is bad enough, even if the attacker did not obtain
full execution control.

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