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CVE-2019-18420

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Date: October 31, 2019

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.

Language: C

Severity Score

Severity Score

Weakness Type (CWE)

Format String Vulnerability

CWE-134

Input Validation

CWE-20

Top Fix

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CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): LOW
User Interaction (UI): NONE
Scope (S): UNCHANGED
Confidentiality (C): NONE
Integrity (I): NONE
Availability (A): HIGH

CVSS v2

Base Score:
Access Vector (AV): NETWORK
Access Complexity (AC): MEDIUM
Authentication (AU): SINGLE
Confidentiality (C): NONE
Integrity (I): NONE
Availability (A): COMPLETE
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