Information

Advisory

XSA-296

Public release

2019-10-31 12:00

Updated

2020-08-14 16:41

Version

5

CVE(s)

CVE-2019-18420

Title

VCPUOP_initialise DoS

Filesadvisory-296.txt (signed advisory file)
xsa296.meta
xsa296.patch
xsa296-4.8.patchAdvisory

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256

        Xen Security Advisory CVE-2019-18420 / XSA-296
                           version 5

                     VCPUOP\_initialise DoS

UPDATES IN VERSION 5

Include recipe for versions 4.12 to 4.9 in xsa296.meta

Canonicalize version text.

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 - xen-unstable xsa296-4.8.patch Xen 4.7 - 4.8

$ sha256sum xsa296* a02e2748870c129691ad2721f916b9cf77b095b6fba292e607eba558ced8dab1 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deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable.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-----

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Xenproject.org Security Team