Date: Mon, 15 Apr 2013 15:55:34 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security@....org> Subject: Xen Security Advisory 48 (CVE-2013-1922) - qemu-nbd format-guessing due to missing format specification -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-1922 / XSA-48 version 2 qemu-nbd format-guessing due to missing format specification UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= The qemu-nbd tool (shipped in the Xen hypervisor tools distribution as qemu-nbd-xen) autodetects the image format. If a particular disk image is intended to be raw, a guest operating system administrator could write a header to the image, describing another format than original one. This could lead to a scenario in which after restart of that guest, qemu-nbd would detect the new apparent format of the image, including a specified backing file or device, which could allow the guest to read any file on the host. IMPACT ====== qemu-nbd (qemu-nbd-xen) is not used by the toolstack software supplied with the Xen tree. However, it is built and installed, and so might be used by host administrators or by toolstacks other than libxl or xend. If qemu-nbd is used, a malicious guest administrator may be able to read any file on the host, depending exactly how. VULNERABLE SYSTEMS ================== For Xen systems using libxl (xl) or xend (xm): if neither qemu-nbd-xen nor qemu-nbd (since qemu-nbd-xen is installed under the latter name in /usr/lib/xen/bin) is explicitly invoked by scripts or other software not supplied by the Xen project, the system is not vulnerable. Xen systems using other toolstacks may be vulnerable if those toolstacks use qemu-nbd[-xen]. A guest administrator who runs qemu-nbd-xen by hand on a guest may be exposing themselves to this vulnerability. Only qemu-xen-upstream is vulnerable; qemu-xen-traditional has a fix which makes this bug not apply. However, the Xen build system builds and installs both by default, in some arbitrary order, to the same filename. So which is installed and might be used is not predictable unless the qemu-xen-upstream build is entirely disabled. Only systems with Xen 4.2 and later installed are vulnerable (by virtue of the presence of Xen) as earlier versions of Xen do not build qemu-xen-upstream at all. MITIGATION ========== No mitigation is available for users of qemu-nbd[-xen]. If you are using qemu-nbd[-xen] from qemu-xen-upstream on raw image files, then arranging to use qemu-xen-traditional instead will fail. If you wish enhanced assurance, removing all copies of of qemu-nbd and qemu-nbd-xen will provide confidence that this vulnerable utility is not being used. RESOLUTION ========== To resolve the problem, it is necessary to apply the attached patch (to the qemu-xen-upstream tree). It is ALSO NECESSARY to ensure that all invocations of qemu-nbd are provided with an appropriate -f (--format) option. Invoking qemu-nbd without this option remains unsafe and the patch does not prevent it. xsa48-4.2.patch Xen 4.2.x (Xen's qemu-upstream-4.2-testing.git) xsa48-unstable.patch Xen unstable (Xen's qemu-upstream-unstable.git) $ sha256sum xsa48* 11e5d1f576770fde67e80e3e8c30f9a1af404fe6d07f1c37e96d68677f31435c xsa48-4.2.patch 20dac78bff584951cb706bb76a3394b47525749655dba2f68a6d923faf168fe8 xsa48-unstable.patch $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJRbBX6AAoJEIP+FMlX6CvZBusIALRc+Cl0DUCJAbGkO8dmzOqA C7F9i1mD5gXZEmj0vBc8DEKivHFy3jgicL+j/SeUVMGouSi/FfntIUcevPHa3R1B 1cPr+oZq9OYZgs/QFbLMPXEeeA0zQiWVJB0AA0h/q+FX5aFE2VpHvi66dcOoBeTL kJHOSEjLmuMEa+Gn1r+Y7nL7XXb5osZKMBoIv5wNX1XNv4PH/yEChTuZ5VD0ScU0 Haib8k2SLDiDiZl/zF/6EdTb/13ceSE7WdBkaJqbbnI8KRbdAc8ERJBuoxupcnAW gPaVwlQ8RrGJrySofoiYozbZcAjbFQAUoxR2Vi6DxB/Lnn7V3PeFEwyXMQcx8ko= =Nel4 -----END PGP SIGNATURE----- [ CONTENT OF TYPE application/octet-stream SKIPPED ] [ CONTENT OF TYPE application/octet-stream SKIPPED ]
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