Date: Tue, 21 Feb 2017 12:00:03 +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 209 (CVE-2017-2620) - cirrus_bitblt_cputovideo does not check if memory region is safe -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2017-2620 / XSA-209 version 3 cirrus_bitblt_cputovideo does not check if memory region is safe UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= In CIRRUS_BLTMODE_MEMSYSSRC mode the bitblit copy routine cirrus_bitblt_cputovideo fails to check wethehr the specified memory region is safe. IMPACT ====== A malicious guest administrator can cause an out of bounds memory write, very likely exploitable as a privilege escalation. VULNERABLE SYSTEMS ================== Versions of qemu shipped with all Xen versions are vulnerable. Xen systems running on x86 with HVM guests, with the qemu process running in dom0 are vulnerable. Only guests provided with the "cirrus" emulated video card can exploit the vulnerability. The non-default "stdvga" emulated video card is not vulnerable. (With xl the emulated video card is controlled by the "stdvga=" and "vga=" domain configuration options.) ARM systems are not vulnerable. Systems using only PV guests are not vulnerable. For VMs whose qemu process is running in a stub domain, a successful attacker will only gain the privileges of that stubdom, which should be only over the guest itself. Both upstream-based versions of qemu (device_model_version="qemu-xen") and `traditional' qemu (device_model_version="qemu-xen-traditional") are vulnerable. MITIGATION ========== Running only PV guests will avoid the issue. Running HVM guests with the device model in a stubdomain will mitigate the issue. Changing the video card emulation to stdvga (stdvga=1, vga="stdvga", in the xl domain configuration) will avoid the vulnerability. CREDITS ======= This issue was discovered by Gerd Hoffmann of Red Hat. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa209-qemuu.patch qemu-xen, qemu upstream (no backport yet) qemu-xen-traditional $ sha256sum xsa209* 167af9ed7163fa7cf4abb52f865290ced3163c7684151bdc1324eb5e534faf13 xsa209-qemut.patch 297578aa43c3e6b21333f1b859fd1d3e68aaaae77b3cadbadd20cfeca8426df3 xsa209-qemuu.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. However, deployment of the "stdvga" mitigation (changing the video card emulation to stdvga) is NOT permitted (except where all the affected systems and VMs are administered and used 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 produces a guest-visible change which will indicate which component contains the vulnerability. Additionally, 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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJYrBl3AAoJEIP+FMlX6CvZ6LMIALETwnX9w8SifkvuYY3jotwp nQWY8ztJkMnai9X10RN6SeVf2dCpXLhATPuPGORgRiZJEuBaGHEsHa00i63FQBSL PaOAgzN1GY+u16Ygv2e3vPcN8mO55A6zcFErF2oLsrfdNsG4pJTwn7bMEjZiqSyG R9xIC6KiA1nojsZO+ynmRvHxFP6epySRayO0PZAGS75LdmEKVxClE3dAeMW77WNv dAs3Qi14hB5BmdryK5f1STk8r2b3UsN1pbvao8odiEWFaB9tPo273gj5RdfnEV3t EzTvH37Q3C4YFoTFx8p6fY5ejHNh4AeSyi9yE7lWtKhDZw56UhdfMmYIgDaKpig= =RBpg -----END PGP SIGNATURE----- Download attachment "xsa209-qemut.patch" of type "application/octet-stream" (1937 bytes) Download attachment "xsa209-qemuu.patch" of type "application/octet-stream" (1934 bytes)
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