How to Fix CVE-2026-23440: Linux (Bundle Sibling)
*By Sai Kiran Pandrala*
Last verified: 2026-05-25
| Severity | CVSS 7.5, High |
|---|---|
| Actively exploited? | No |
| Affected | Linux (fef06678931ff67b158d337b581e5cf5ca40a3a3 < 3dffc083292e6872787bd7e34b957627622f9af4, fef06678931ff67b158d337b581e5cf5ca40a3a3 < 2051c709dce92da3550040aa7949cd5a9c89b14e); Linux (6.4, 0 < 6.4) |
| Fixed in | Same patched build as CVE-2026-23401 |
| Type (CWE) | Not verified |
CVE-2026-23440 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-2026-23440 matches the primary write-up.
What is different about CVE-2026-23440?
In the Linux kernel, the following vulnerability has been resolved:
net/mlx5e: Fix race condition during IPSec ESN update
In IPSec full offload mode, the device reports an ESN (Extended
Sequence Number) wrap event to the driver. The driver validates this
event by querying the IPSec ASO and checking that the esn_event_arm
field is 0x0, which indicates an event has occurred. After handling
the event, the driver must re-arm the context by setting esn_event_arm
back to 0x1.
Impact is consistent with the bundle: exploitation of a race condition that can corrupt memory or state. The patched build closes every code path in the advisory in one update.
How to fix CVE-2026-23440
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-2026-23440 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-2026-23440?
CVSS rates it 7.5 (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-2026-23440 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/3dffc083292e6872787bd7e34b957627622f9af4
- NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2026-23440
- 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.*