VulnerabilityPublished 3 Apr 2026Updated 19 Oct 2026

CVE-2026-23440: Linux kernel · net/mlx5e: Fix race condition during IPSec ESN update

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 7.5 High · fixed in beb6e2e5976a128b0cccf10d158124422210c5ef : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS

0.2% chance of exploitation in 30 days – higher than 18% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-16.

Patch

Available – fixed in beb6e2e5976a128b0cccf10d158124422210c5ef, 2051c709dce92da3550040aa7949cd5a9c89b14e, 96c9c25b74686ac2de15921c9ad30c5ef13af8cd +2

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ fef06678931ff67b158d337b581e5cf5ca40a3a3, < beb6e2e5976a128b0cccf10d158124422210c5ef	Fixed in beb6e2e5976a128b0cccf10d158124422210c5ef
LinuxLinux	Affected ≥ fef06678931ff67b158d337b581e5cf5ca40a3a3, < 2051c709dce92da3550040aa7949cd5a9c89b14e	Fixed in 2051c709dce92da3550040aa7949cd5a9c89b14e
LinuxLinux	Affected ≥ fef06678931ff67b158d337b581e5cf5ca40a3a3, < 96c9c25b74686ac2de15921c9ad30c5ef13af8cd	Fixed in 96c9c25b74686ac2de15921c9ad30c5ef13af8cd
LinuxLinux	Affected ≥ fef06678931ff67b158d337b581e5cf5ca40a3a3, < 8d625c15471fb8780125eaef682983a96af77bdc	Fixed in 8d625c15471fb8780125eaef682983a96af77bdc
LinuxLinux	Affected ≥ fef06678931ff67b158d337b581e5cf5ca40a3a3, < 3dffc083292e6872787bd7e34b957627622f9af4	Fixed in 3dffc083292e6872787bd7e34b957627622f9af4
LinuxLinux	Affected =6.4	Fixed in–

AI-suggested

A fix is available in the Linux kernel. The vulnerability is resolved by re-arming the ESN event immediately after validation before updating the xfrm state, preventing duplicate event processing. Users should update to the fixed Linux kernel version 6.4 or later containing the patch identified by the provided commit hashes.

Description

CVE-2026-23440 is a race condition vulnerability in the Linux kernel's mlx5e driver affecting IPSec full offload mode. The flaw occurs during the handling of Extended Sequence Number (ESN) wrap events, where a race condition can cause the ESN high-order bits to be incremented incorrectly. This leads to the hardware being programmed with an invalid ESN state, resulting in anti-replay failures and a complete halt of IPSec traffic. The issue is fixed by re-arming the ESN event immediately after validation to prevent duplicate processing.

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
Architecture and Design
In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
Architecture and Design
Use thread-safe capabilities such as the data access abstraction in Spring.
Architecture and Design
Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V1.11.2 (opens in a new tab)
Attack patterns
Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions (opens in a new tab)
Leveraging Race Conditions (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 13:07 UTC

WeaknessesCWE-362

Technical details

References

Community reviews

Related threats