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CVE-2019-18423

Published: 31 October 2019

An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service via a XENMEM_add_to_physmap hypercall. p2m->max_mapped_gfn is used by the functions p2m_resolve_translation_fault() and p2m_get_entry() to sanity check guest physical frame. The rest of the code in the two functions will assume that there is a valid root table and check that with BUG_ON(). The function p2m_get_root_pointer() will ignore the unused top bits of a guest physical frame. This means that the function p2m_set_entry() will alias the frame. However, p2m->max_mapped_gfn will be updated using the original frame. It would be possible to set p2m->max_mapped_gfn high enough to cover a frame that would lead p2m_get_root_pointer() to return NULL in p2m_get_entry() and p2m_resolve_translation_fault(). Additionally, the sanity check on p2m->max_mapped_gfn is off-by-one allowing "highest mapped + 1" to be considered valid. However, p2m_get_root_pointer() will return NULL. The problem could be triggered with a specially crafted hypercall XENMEM_add_to_physmap{, _batch} followed by an access to an address (via hypercall or direct access) that passes the sanity check but cause p2m_get_root_pointer() to return NULL. A malicious guest administrator may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen version 4.8 and newer are vulnerable. Only Arm systems are vulnerable. x86 systems are not affected.

Notes

AuthorNote
mdeslaur
hypervisor packages are in universe. For
issues in the hypervisor, add appropriate
tags to each section, ex:
Tags_xen: universe-binary

Priority

Medium

Cvss 3 Severity Score

8.8

Score breakdown

Status

Package Release Status
xen
Launchpad, Ubuntu, Debian
bionic Needed

disco Ignored
(end of life)
eoan Ignored
(end of life)
focal Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
groovy Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
hirsute Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
impish Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
jammy Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
kinetic Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
lunar Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
mantic Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
noble Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
trusty Does not exist

upstream Needs triage

xenial Needed

Binaries built from this source package are in Universe and so are supported by the community.

Severity score breakdown

Parameter Value
Base score 8.8
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H