Alpine: xen: security update to 4.13.1-r2

high Tenable Self-Hosted Container Security Plugin ID 407770

Description

There are packages installed that are affected by multiple vulnerabilities referenced in the following CVEs:

- An issue was discovered in Xen through 4.13.x, allowing x86 HVM guest OS users to cause a hypervisor
crash. An inverted conditional in x86 HVM guests' dirty video RAM tracking code allows such guests to make
Xen de-reference a pointer guaranteed to point at unmapped space. A malicious or buggy HVM guest may cause
the hypervisor to crash, resulting in Denial of Service (DoS) affecting the entire host. Xen versions from
4.8 onwards are affected. Xen versions 4.7 and earlier are not affected. Only x86 systems are affected.
Arm systems are not affected. Only x86 HVM guests using shadow paging can leverage the vulnerability. In
addition, there needs to be an entity actively monitoring a guest's video frame buffer (typically for
display purposes) in order for such a guest to be able to leverage the vulnerability. x86 PV guests, as
well as x86 HVM guests using hardware assisted paging (HAP), cannot leverage the vulnerability.
(CVE-2020-15563)

- An issue was discovered in Xen through 4.13.x, allowing Arm guest OS users to cause a hypervisor crash
because of a missing alignment check in VCPUOP_register_vcpu_info. The hypercall VCPUOP_register_vcpu_info
is used by a guest to register a shared region with the hypervisor. The region will be mapped into Xen
address space so it can be directly accessed. On Arm, the region is accessed with instructions that
require a specific alignment. Unfortunately, there is no check that the address provided by the guest will
be correctly aligned. As a result, a malicious guest could cause a hypervisor crash by passing a
misaligned address. A malicious guest administrator may cause a hypervisor crash, resulting in a Denial of
Service (DoS). All Xen versions are vulnerable. Only Arm systems are vulnerable. x86 systems are not
affected. (CVE-2020-15564)

- An issue was discovered in Xen through 4.13.x, allowing x86 Intel HVM guest OS users to cause a host OS
denial of service or possibly gain privileges because of insufficient cache write-back under VT-d. When
page tables are shared between IOMMU and CPU, changes to them require flushing of both TLBs. Furthermore,
IOMMUs may be non-coherent, and hence prior to flushing IOMMU TLBs, a CPU cache also needs writing back to
memory after changes were made. Such writing back of cached data was missing in particular when splitting
large page mappings into smaller granularity ones. A malicious guest may be able to retain read/write DMA
access to frames returned to Xen's free pool, and later reused for another purpose. Host crashes (leading
to a Denial of Service) and privilege escalation cannot be ruled out. Xen versions from at least 3.2
onwards are affected. Only x86 Intel systems are affected. x86 AMD as well as Arm systems are not
affected. Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device
assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table
sharing will be enabled (by default) only if Xen considers IOMMU and CPU large page size support
compatible. (CVE-2020-15565)

- An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a host OS crash because of
incorrect error handling in event-channel port allocation. The allocation of an event-channel port may
fail for multiple reasons: (1) port is already in use, (2) the memory allocation failed, or (3) the port
we try to allocate is higher than what is supported by the ABI (e.g., 2L or FIFO) used by the guest or the
limit set by an administrator (max_event_channels in xl cfg). Due to the missing error checks, only (1)
will be considered an error. All the other cases will provide a valid port and will result in a crash when
trying to access the event channel. When the administrator configured a guest to allow more than 1023
event channels, that guest may be able to crash the host. When Xen is out-of-memory, allocation of new
event channels will result in crashing the host rather than reporting an error. Xen versions 4.10 and
later are affected. All architectures are affected. The default configuration, when guests are created
with xl/libxl, is not vulnerable, because of the default event-channel limit. (CVE-2020-15566)

- An issue was discovered in Xen through 4.13.x, allowing Intel guest OS users to gain privileges or cause a
denial of service because of non-atomic modification of a live EPT PTE. When mapping guest EPT (nested
paging) tables, Xen would in some circumstances use a series of non-atomic bitfield writes. Depending on
the compiler version and optimisation flags, Xen might expose a dangerous partially written PTE to the
hardware, which an attacker might be able to race to exploit. A guest administrator or perhaps even an
unprivileged guest user might be able to cause denial of service, data corruption, or privilege
escalation. Only systems using Intel CPUs are vulnerable. Systems using AMD CPUs, and Arm systems, are not
vulnerable. Only systems using nested paging (hap, aka nested paging, aka in this case Intel EPT) are
vulnerable. Only HVM and PVH guests can exploit the vulnerability. The presence and scope of the
vulnerability depends on the precise optimisations performed by the compiler used to build Xen. If the
compiler generates (a) a single 64-bit write, or (b) a series of read-modify-write operations in the same
order as the source code, the hypervisor is not vulnerable. For example, in one test build using GCC 8.3
with normal settings, the compiler generated multiple (unlocked) read-modify-write operations in source-
code order, which did not constitute a vulnerability. We have not been able to survey compilers;
consequently we cannot say which compiler(s) might produce vulnerable code (with which code-generation
options). The source code clearly violates the C rules, and thus should be considered vulnerable.
(CVE-2020-15567)

Plugin Details

Severity: High

ID: 407770

Version: Revision 1.29

Type: Local

Family: Alpine Linux Local Security Checks

Published: 10/31/2023

Updated: 7/2/2026

Supported Sensors: Agentless Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security

Risk Information

VPR

Risk Factor: Medium

Score: 5

Percentile: 95.11

CVSS v2

Risk Factor: Medium

Base Score: 6.1

Temporal Score: 4.5

Vector: CVSS2#AV:L/AC:L/Au:N/C:P/I:P/A:C

CVSS Score Source: CVE-2020-15565

CVSS v3

Risk Factor: High

Base Score: 8.8

Temporal Score: 7.7

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 7/7/2020

Reference Information

CVE: CVE-2020-15563, CVE-2020-15564, CVE-2020-15565, CVE-2020-15566, CVE-2020-15567

IAVB: 2020-B-0034-S

Detections

Analytics