Bug 1771366 (CVE-2019-18420)

Summary: CVE-2019-18420 xen: allows guest OS users to cause denial of service via VCPUOP_initialise hypercall
Product: [Other] Security Response Reporter: Dhananjay Arunesh <darunesh>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: acaringi, ailan, bhu, brdeoliv, dhoward, drjones, dvlasenk, fhrbata, hkrzesin, imammedo, jforbes, jshortt, jstancek, knoel, m.a.young, mrezanin, nmurray, pbonzini, rkrcmar, robinlee.sysu, rvrbovsk, vkuznets, xen-maint
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Last Closed: 2020-02-18 17:58:51 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 1771368    
Bug Blocks: 1771369    

Description Dhananjay Arunesh 2019-11-12 09:14:15 UTC 
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.

Reference:
http://www.openwall.com/lists/oss-security/2019/10/31/1
Comment 1 Dhananjay Arunesh 2019-11-12 09:15:12 UTC 
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1771368]
Comment 2 Dhananjay Arunesh 2019-11-12 09:15:51 UTC 
External References:

http://xenbits.xen.org/xsa/advisory-296.html