Google: sys-kernel/cchost-kernel-6_12, sys-kernel/csql-kernel-6_12: security update to 19506.120.52

medium Tenable Cloud Security Plugin ID 469531

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

- In the Linux kernel, the following vulnerability has been resolved: x86/cpu: Remove X86_CR4_FRED from the
CR4 pinned bits mask Commit in Fixes added the FRED CR4 bit to the CR4 pinned bits mask so that whenever
something else modifies CR4, that bit remains set. Which in itself is a perfectly fine idea. However,
there's an issue when during boot FRED is initialized: first on the BSP and later on the APs. Thus,
there's a window in time when exceptions cannot be handled. This becomes particularly nasty when running
as SEV-{ES,SNP} or TDX guests which, when they manage to trigger exceptions during that short window
described above, triple fault due to FRED MSRs not being set up yet. See Link tag below for a much more
detailed explanation of the situation. So, as a result, the commit in that Link URL tried to address this
shortcoming by temporarily disabling CR4 pinning when an AP is not online yet. However, that is a problem
in itself because in this case, an attack on the kernel needs to only modify the online bit - a single bit
in RW memory - and then disable CR4 pinning and then disable SM*P, leading to more and worse things to
happen to the system. So, instead, remove the FRED bit from the CR4 pinning mask, thus obviating the need
to temporarily disable CR4 pinning. If someone manages to disable FRED when poking at CR4, then
idt_invalidate() would make sure the system would crash'n'burn on the first exception triggered, which is
a much better outcome security-wise. (CVE-2026-31561)

Solution

Update the sys-kernel/cchost-kernel-6_12 library and its related packages to version 19506.120.52 or later.

Plugin Details

Severity: Medium

ID: 469531

Version: Revision 1.3

Type: Local

Family: Google COS Security Checks

Published: 10/3/2026

Updated: 10/6/2026

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

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.75

Vendor

Vendor Severity: LOW

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

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

CVSS Score Source: CVE-2026-31561

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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: 4/24/2026

Reference Information

CVE: CVE-2026-31561

Detections

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