How to Fix CVE-2026-31396: Linux (Bundle Sibling)

*By Sai Kiran Pandrala*

Last verified: 2026-05-25

CVE-2026-31396 is a sibling vulnerability in the same Linux Linux advisory bundle as CVE-2026-23401. The same patched build closes every CVE in the bundle, so the remediation procedure for CVE-2026-31396 matches the primary write-up.

What is different about CVE-2026-31396?

In the Linux kernel, the following vulnerability has been resolved:

net: macb: fix use-after-free access to PTP clock

PTP clock is registered on every opening of the interface and destroyed on

every closing. However it may be accessed via get_ts_info ethtool call

which is possible while the interface is just present in the kernel. BUG: KASAN: use-after-free in ptp_clock_index+0x47/0x50 drivers/ptp/ptp_clock.c:426

Read of size 4 at addr ffff8880194345cc by task syz.0.6/948

CPU: 1 PID: 948 C...

Impact is consistent with the bundle: use-after-free that can lead to heap corruption and code execution. The patched build closes every code path in the advisory in one update.

How to fix CVE-2026-31396

Apply the patched build per the primary write-up: How to Fix CVE-2026-23401.

For a quick check, confirm the running version of Linux:

# Confirm the installed version via your package manager
dpkg -l | grep -i linux   # Debian/Ubuntu
rpm -qa | grep -i linux   # RHEL/CentOS/Rocky

Frequently asked questions

Is CVE-2026-31396 being actively exploited?

Not at the time of writing. It is not listed in CISA's Known Exploited Vulnerabilities catalog. That status can change, so monitor the vendor advisory and the KEV catalog if the system is exposed.

How severe is CVE-2026-31396?

CVSS rates it 7.8 (High). Use that score to set your patch priority alongside the other items in your queue.

Do I have to take Linux offline to apply the patch?

It depends on the deployment. High-availability or clustered installs can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.

What if my vulnerability scanner still flags CVE-2026-31396 after I patch?

Re-run the scan after a service restart, then confirm the scanner's plugin set is up to date. Some scanners detect by banner version only and lag the official fix metadata by a release.

References

• Official vendor advisory: https://git.kernel.org/stable/c/8820ffe0975fd2efbe50453e9179c8e1c33a13d3
• NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2026-31396
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Primary write-up: How to Fix CVE-2026-23401

*Written by Sai Kiran Pandrala. Last verified 2026-05-25. Part of the Linux Linux advisory bundle. Full procedure at how-to-fix-cve-2026-23401.*