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Date: Fri, 07 Sep 2012 19:33:42 +0000
From: "Nathan March" <>
To: " security team" <>,,,
Cc: " security team" <>
Subject: Re: [Xen-users] Xen Security Advisory 17 (CVE-2012-3515) - Qemu VT100
 emulation vulnerability

´╗┐Hi All,

I'm guessing this wasn't intentional, but the patch for xsa17 does not 
contain a complete path to the tools/ioemu-qemu-xen/ path:

--- a/console.c
+++ b/console.c

Compared to all the other patches which provide a full path to the 
patched file:

--- a/xen/include/asm-x86/debugreg.h Mon Aug 06 12:28:03 2012 +0100
+++ b/xen/include/asm-x86/debugreg.h Wed Aug 15 12:00:21 2012 +0100

Little annoying since it means you have to track down which console.c 
is being patched instead of just applying from the root xen build dir.

- Nathan

------ Original Message ------
From: " security team" <>
Cc: " security team" <>
Sent: 9/5/2012 4:12:47 AM
Subject: [Xen-users] Xen Security Advisory 17 (CVE-2012-3515) - Qemu 
VT100 emulation vulnerability
>Hash: SHA1
>           Xen Security Advisory CVE-2012-3515 / XSA-17
>                          version 2
>              Qemu VT100 emulation vulnerability
>Public release.
>The device model used by fully virtualised (HVM) domains, qemu, does
>not properly handle escape VT100 sequences when emulating certain
>devices with a virtual console backend.
>An attacker who has sufficient privilege to access a vulnerable device
>within a guest can overwrite portions of the device model's address
>space. This can allow them to escalate their privileges to that of the
>device model process.
>All Xen systems running HVM guests are potentially vulnerable to this
>depending on the specific guest configuration. The default
>configuration is vulnerable.
>Guests using either the traditional "qemu-xen" or upstream qemu device
>models are vulnerable.
>This issue can be avoided by only running PV guests or by configuring
>HVM guests to not use the virtual console('vc') backend for any device.
>For serial devices specify in your guest configuration:
>    serial = 'none'
>in your guest configuration.
>For parallel port devices the syntax is toolstack specific.
>For xend specify in your guest configuration:
>    parallel = 'none'
>For xl specify in your guest configuration:
>    xl: device_model_args = ['-parallel', 'none']
>In both cases the default is to use the vulnerable 'vc' mode.
>You can confirm whether or not you are vulnerable by pressing
>Ctrl-Alt-<N> (for digit N) while connected to either the VNC or SDL
>console. If you are able to switch to a window displaying "serial" or
>"parallel" then you are vulnerable.
>The issue can also be mitigated by enabling the stub domain device
>model. In this case the attacked can only potentially gain control of
>the stub domain and not of the entire system.
>To enable stub domains specify in your guest configuration:
>   device_model = "stubdom-dm"
>Applying the appropriate attached patch(es) will resolve the issue.
>The attached patches resolve this issue
>Traditional qemu tree
>  Xen 4.0, 4.1 and unstable         xsa17-qemu-xen-traditional-all.patch
>Upstream qemu tree (present in unstable only)
>  Xen unstable                      xsa17-qemu-xen-unstable.patch
>$ sha256sum xsa17-*.patch
>60215322d3fbbc2054dfc160a20d9e0811af88487c4edc2f6ea81dcd5cedf039  xsa17-qemu-xen-traditional-all.patch
>7b4bb59e7757080e7806a8b8eeb6b78fa0ffdfbfb28a7a379f7edff285bffd88  xsa17-qemu-xen-unstable.patch
>Version: GnuPG v1.4.10 (GNU/Linux)

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