Use of Externally-Controlled Format String Affecting xen package, versions <4.11.3+24-g14b62ab3e5-1


Severity

Recommended
0.0
medium
0
10

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Threat Intelligence

EPSS
2.52% (83rd percentile)

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  • Snyk IDSNYK-ECHOLATEST-XEN-18388795
  • published29 Jul 2026
  • disclosed31 Oct 2019

Introduced: 31 Oct 2019

CVE-2019-18420  (opens in a new tab)
CWE-134  (opens in a new tab)

How to fix?

Upgrade Echo:latest xen to version 4.11.3+24-g14b62ab3e5-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream xen package and not the xen package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1