Xen: Security Vulnerabilities
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]
There are two issues related to the mapping of pages belonging to other
domains: For one, an assertion is wrong there, where the case actually
needs handling. A NULL pointer de-reference could result on a release
build. This is CVE-2025-58144.
And then the P2M lock isn't held until a page reference was actually
obtained (or the attempt to do so has failed). Otherwise the page can
not only change type, but even ownership in between, thus allowing
domain boundaries to be violated. This is CVE-2025-58145.
CVSS Score
7.5
EPSS Score
0.0
Published
2025-09-11
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]
There are multiple issues related to the handling and accessing of guest
memory pages in the viridian code:
1. A NULL pointer dereference in the updating of the reference TSC area.
This is CVE-2025-27466.
2. A NULL pointer dereference by assuming the SIM page is mapped when
a synthetic timer message has to be delivered. This is
CVE-2025-58142.
3. A race in the mapping of the reference TSC page, where a guest can
get Xen to free a page while still present in the guest physical to
machine (p2m) page tables. This is CVE-2025-58143.
CVSS Score
9.8
EPSS Score
0.0
Published
2025-09-11
When setting up interrupt remapping for legacy PCI(-X) devices,
including PCI(-X) bridges, a lookup of the upstream bridge is required.
This lookup, itself involving acquiring of a lock, is done in a context
where acquiring that lock is unsafe. This can lead to a deadlock.
CVSS Score
7.5
EPSS Score
0.001
Published
2025-07-17
Certain instructions need intercepting and emulating by Xen. In some
cases Xen emulates the instruction by replaying it, using an executable
stub. Some instructions may raise an exception, which is supposed to be
handled gracefully. Certain replayed instructions have additional logic
to set up and recover the changes to the arithmetic flags.
For replayed instructions where the flags recovery logic is used, the
metadata for exception handling was incorrect, preventing Xen from
handling the the exception gracefully, treating it as fatal instead.
CVSS Score
4.3
EPSS Score
0.001
Published
2025-07-16
For a brief summary of Xapi terminology, see:
https://xapi-project.github.io/xen-api/overview.html#object-model-overview
Xapi contains functionality to backup and restore metadata about Virtual
Machines and Storage Repositories (SRs).
The metadata itself is stored in a Virtual Disk Image (VDI) inside an
SR. This is used for two purposes; a general backup of metadata
(e.g. to recover from a host failure if the filer is still good), and
Portable SRs (e.g. using an external hard drive to move VMs to another
host).
Metadata is only restored as an explicit administrator action, but
occurs in cases where the host has no information about the SR, and must
locate the metadata VDI in order to retrieve the metadata.
The metadata VDI is located by searching (in UUID alphanumeric order)
each VDI, mounting it, and seeing if there is a suitable metadata file
present. The first matching VDI is deemed to be the metadata VDI, and
is restored from.
In the general case, the content of VDIs are controlled by the VM owner,
and should not be trusted by the host administrator.
A malicious guest can manipulate its disk to appear to be a metadata
backup.
A guest cannot choose the UUIDs of its VDIs, but a guest with one disk
has a 50% chance of sorting ahead of the legitimate metadata backup. A
guest with two disks has a 75% chance, etc.
CVSS Score
3.8
EPSS Score
0.001
Published
2025-02-14
The hypervisor contains code to accelerate VGA memory accesses for HVM
guests, when the (virtual) VGA is in "standard" mode. Locking involved
there has an unusual discipline, leaving a lock acquired past the
return from the function that acquired it. This behavior results in a
problem when emulating an instruction with two memory accesses, both of
which touch VGA memory (plus some further constraints which aren't
relevant here). When emulating the 2nd access, the lock that is already
being held would be attempted to be re-acquired, resulting in a
deadlock.
This deadlock was already found when the code was first introduced, but
was analysed incorrectly and the fix was incomplete. Analysis in light
of the new finding cannot find a way to make the existing locking
discipline work.
In staging, this logic has all been removed because it was discovered
to be accidentally disabled since Xen 4.7. Therefore, we are fixing the
locking problem by backporting the removal of most of the feature. Note
that even with the feature disabled, the lock would still be acquired
for any accesses to the VGA MMIO region.
CVSS Score
6.5
EPSS Score
0.002
Published
2024-12-19
PVH guests have their ACPI tables constructed by the toolstack. The
construction involves building the tables in local memory, which are
then copied into guest memory. While actually used parts of the local
memory are filled in correctly, excess space that is being allocated is
left with its prior contents.
CVSS Score
5.5
EPSS Score
0.001
Published
2024-12-19
Certain PCI devices in a system might be assigned Reserved Memory
Regions (specified via Reserved Memory Region Reporting, "RMRR") for
Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used
for platform tasks such as legacy USB emulation.
Since the precise purpose of these regions is unknown, once a device
associated with such a region is active, the mappings of these regions
need to remain continuouly accessible by the device. In the logic
establishing these mappings, error handling was flawed, resulting in
such mappings to potentially remain in place when they should have been
removed again. Respective guests would then gain access to memory
regions which they aren't supposed to have access to.
CVSS Score
7.5
EPSS Score
0.001
Published
2024-09-25
When multiple devices share resources and one of them is to be passed
through to a guest, security of the entire system and of respective
guests individually cannot really be guaranteed without knowing
internals of any of the involved guests. Therefore such a configuration
cannot really be security-supported, yet making that explicit was so far
missing.
Resources the sharing of which is known to be problematic include, but
are not limited to
- - PCI Base Address Registers (BARs) of multiple devices mapping to the
same page (4k on x86),
- - INTx lines.
CVSS Score
7.5
EPSS Score
0.001
Published
2024-09-25
In x86's APIC (Advanced Programmable Interrupt Controller) architecture,
error conditions are reported in a status register. Furthermore, the OS
can opt to receive an interrupt when a new error occurs.
It is possible to configure the error interrupt with an illegal vector,
which generates an error when an error interrupt is raised.
This case causes Xen to recurse through vlapic_error(). The recursion
itself is bounded; errors accumulate in the the status register and only
generate an interrupt when a new status bit becomes set.
However, the lock protecting this state in Xen will try to be taken
recursively, and deadlock.
CVSS Score
7.3
EPSS Score
0.005
Published
2024-09-25