Date: Thu, 31 Oct 2019 12:29:09 +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 296 v4 (CVE-2019-18420) - VCPUOP_initialise DoS -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2019-18420 / XSA-296 version 4 VCPUOP_initialise DoS UPDATES IN VERSION 4 ==================== Public release. ISSUE DESCRIPTION ================= hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created. IMPACT ====== Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (Dos). VULNERABLE SYSTEMS ================== Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability. MITIGATION ========== There are no mitigations. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa296.patch Xen 4.9 ... unstable xsa296-4.8.patch Xen 4.7 ... 4.8 $ sha256sum xsa296* 71bd433f788dd511fad90165bc5ba9bcabe949eecd912f2a616e3c996960d67d xsa296.meta ccfd81b162b8535d952f56b1f87dfdd960e71bf07c1cf8388976e78e2e86cde5 xsa296.patch b283be3df6789402553172b7fd582bfffb4fa72a6b33543439bd2fb1b87bfbd4 xsa296-4.8.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----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAl2600kMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZn10IAKQhLY9RfkgZhY/6cACYnXqFGWhS6MvyeZrVs1L4 BaojMJilpAo7kc9Xcf+0ThxKI5M/eEeDUdGjFHfBtOUrjOAhaZjaYI1paJwX0JEV QoAMQERTtopFnkCNtvykrMiKZQ2xp6hiios+32PvDdVnjO+rkrKESRNoBVNYlC1f qN8SbZ6m0C5jP4C82ifDEeJHJsVJtfYQSeRl95pgCmsmxxd3x7q7ubPcR6kizT5t Bu4sAtrWNF5zaBrb5kL29yohn4oBLmMV5NO0hSlCbR3FgeFZ7LTwiz8y4d7tVSHg fjbsvhmhfhYO1OnZWFea3QXMgfZjsg6qq9jBnpmGu35WVMY= =xUlU -----END PGP SIGNATURE----- Download attachment "xsa296.meta" of type "application/octet-stream" (1390 bytes) Download attachment "xsa296.patch" of type "application/octet-stream" (7744 bytes) Download attachment "xsa296-4.8.patch" of type "application/octet-stream" (7767 bytes)
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