CVE ID:	CVE-2019-18420
Description:	An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall. 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. Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (DoS). 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.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2019-18420 Bugtraq: 20200114 [SECURITY] [DSA 4602-1] xen security update (Google Search) https://seclists.org/bugtraq/2020/Jan/21 Debian Security Information: DSA-4602 (Google Search) https://www.debian.org/security/2020/dsa-4602 https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/I5WWPW4BSZDDW7VHU427XTVXV7ROOFFW/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/2BQKX7M2RHCWDBKNPX4KEBI3MJIH6AYZ/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/IZYATWNUGHRBG6I3TC24YHP5Y3J7I6KH/ https://security.gentoo.org/glsa/202003-56 http://xenbits.xen.org/xsa/advisory-296.html http://www.openwall.com/lists/oss-security/2019/10/31/1 SuSE Security Announcement: openSUSE-SU-2019:2506 (Google Search) http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00037.html