Date: Wed, 27 Jun 2018 21:03:58 +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-team-members@....org> Subject: Xen Security Advisory 265 (CVE-2018-12893) - x86: #DB exception safety check can be triggered by a guest -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2018-12893 / XSA-265 version 3 x86: #DB exception safety check can be triggered by a guest UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= One of the fixes in XSA-260 added some safety checks to help prevent Xen livelocking with debug exceptions. Unfortunately, due to an oversight, at least one of these safety checks can be triggered by a guest. IMPACT ====== A malicious PV guest can crash Xen, leading to a Denial of Service. VULNERABLE SYSTEMS ================== All Xen systems which have applied the XSA-260 fix are vulnerable. Only x86 systems are vulnerable. ARM systems are not vulnerable. Only x86 PV guests can exploit the vulnerability. x86 HVM and PVH guests cannot exploit the vulnerability. An attacker needs to be able to control hardware debugging facilities to exploit the vulnerability, but such permissions are typically available to unprivileged users. MITIGATION ========== Running only x86 HVM or PVH guests will avoid the vulnerability. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa265.patch xen-unstable, Xen 4.10.x, 4.9.x, 4.8.x xsa265-4.7.patch Xen 4.7.x, 4.6.x $ sha256sum xsa265* 3eb66ed7251dcc4259eeffe608b2747857e269307d894a1cb950973420184aa7 xsa265.patch 00faf2a4159698b6540565ece06de103c3547855e2084324ca44772b8a24aa18 xsa265-4.7.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or mitigations 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: 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 iQEcBAEBCAAGBQJbM+5JAAoJEIP+FMlX6CvZtSgIAMF8d/3Jor6b0EbW55JSLh76 56I8QfkqX4Xv/yWri3sXGJmPz7Af/qjDO+Ix5IScq54ugN5C8z7OBcbXFpX1WxNJ xCv6QjsbPmGCZHsT+NdWrl/ac6ZH3xlhE+S1awQ+9SkC+r6bRH/iROO+4DhpYQde CGoyYIwFq2VJoovh8lWHMsVl8VUXisyDk3bPK17VlAEFF1LuOkaan1UGEKRsciGX 12IlNw/I6c8a85wWpFtph1AOVZfrodWdwyj8vgLY3MHnEs+86/cm5O4+GxKHezHf P5dJDZ38HBPRL1qC+yFRV2sLxLgrc7fYlSWr3/xtOGo23aDLjCvS+FsMfIpyjPQ= =sf+j -----END PGP SIGNATURE----- Download attachment "xsa265.patch" of type "application/octet-stream" (4564 bytes) Download attachment "xsa265-4.7.patch" of type "application/octet-stream" (4558 bytes)
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