xen-4.4.2-2, available from the virt6-testing repository, includes the fix for this issue.
Note that Xen actually does attempt to disable the floppy disk for HVM domains by default, but due to a bug in qemu, the floppy disk only partially disabled; enough functionality to exploit this bug remains.
This should be available from the normal xen4 repositories sometime this afternoon.
-George
---------- Forwarded message ---------- From: Xen.org security team security@xen.org Date: Wed, May 13, 2015 at 12:16 PM Subject: [Xen-users] Xen Security Advisory 133 (CVE-2015-3456) - Privilege escalation via emulated floppy disk drive To: xen-announce@lists.xen.org, xen-devel@lists.xen.org, xen-users@lists.xen.org, oss-security@lists.openwall.com Cc: "Xen.org security team" security@xen.org
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Xen Security Advisory CVE-2015-3456 / XSA-133 version 2
Privilege escalation via emulated floppy disk drive
UPDATES IN VERSION 2 ====================
Public release.
ISSUE DESCRIPTION =================
The code in qemu which emulates a floppy disk controller did not correctly bounds check accesses to an array and therefore was vulnerable to a buffer overflow attack.
IMPACT ======
A guest which has access to an emulated floppy device can exploit this vulnerability to take over the qemu process elevating its privilege to that of the qemu process.
VULNERABLE SYSTEMS ==================
All Xen systems running x86 HVM guests without stubdomains are 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.
Guests using a qemu-dm stubdomain to run the device model are only vulnerable to takeover of that service domain.
Systems running only x86 PV guests are not vulnerable.
ARM systems are not vulnerable.
MITIGATION ==========
Enabling stubdomains will mitigate this issue, by reducing the escalation to only those privileges accorded to the service domain.
qemu-dm stubdomains are only available with the traditional "qemu-xen" version.
CREDITS =======
This issue was discovered by Jason Geffner, Senior Security Researcher at CrowdStrike.
RESOLUTION ==========
Applying the appropriate attached patch resolves this issue.
xsa133-qemuu.patch qemu-upstream-unstable, Xen 4.5.x, Xen 4.4.x xsa133-qemuu-4.3-4.2.patch qemu-upstream-unstable, Xen 4.3.x, Xen 4.2.x xsa133-qemut.patch qemu-xen-unstable, Xen 4.5.x, Xen 4.4.x, Xen 4.3.x, Xen 4.2.x
$ sha256sum xsa133*.patch e7ca0106a9d4bfe472b3b52bbed8646b47305634ff16c3e17ed6185296a7e7ff xsa133-qemut.patch 0cbc0415ef63bc195a0338441f3770d9fe6741e894879e35d1a6609ad028e42f xsa133-qemuu.patch cf735c1ecb6a40ca57d408e5c01725eca5b9b0a14b1d31b4362dc3f036bdeb28 xsa133-qemuu-4.3-4.2.patch $
DEPLOYMENT DURING EMBARGO =========================
Deployment of the patches described above (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators.
But: Deployment of the mitigation by enabling stubdomains is NOT permitted (except on systems used and administered only by organisations which are members of the Xen Project Security Issues Predisclosure List). Specifically, deployment on public cloud systems is NOT permitted. This is because this configuration change may be visible to the guest.
Also, distribution of updated software is prohibited (except to other members of the predisclosure list).
Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team.
(Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.)
For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html
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