HighCVE-2026-53239

Linux Kernel: Use-After-Free (CVE-2026-53239)

Published 25.06.2026Last modified 19.10.2026Sources: SUSE, Siemens ProductCERT, Debian LTS, Ubuntu, Red Hat, BSI, CVE.org, Msrc Update Guide

What is affected, what to do

A flaw was found in the Linux kernel. A race condition exists in the `xfrm` policy handling, specifically within the `xfrm_policy_bysel_ctx()` function.

Update Linux Kernel to version 5.10.259, Linux Kernel to version 5.15.210, Linux Kernel to version 6.1.176.

Affected: Linux Kernel lt 5.0..5.10.259
Linux Kernel lt 5.11..5.15.210
Linux Kernel lt 5.16..6.1.176
Linux Kernel lt 6.2..6.6.143
Linux Kernel lt 6.7..6.12.94
Linux Kernel lt 6.13..6.18.36
Linux Kernel lt 6.19..7.0.13
Fixed in: Linux Kernel 5.10.259
Linux Kernel 5.15.210
Linux Kernel 6.1.176
Linux Kernel 6.6.143
Linux Kernel 6.12.94
Linux Kernel 6.18.36
Linux Kernel 7.0.13
Linux Kernel 7.1

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

7.8

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v3

7.8

CVSS v3

Severity High on the scale from 0 to 10.

Source: SUSE, Siemens ProductCERT, Debian LTS, Ubuntu, Red Hat, BSI, CVE.org, Msrc Update Guide

0.1 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 0.9

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 58.53 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.8 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.8
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.1 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 0.9; Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 25.06.2026
CISA assessment (SSVC): Exploitation: none known · not automatable · Technical impact: total; Source: CISA Vulnrichment, as of 16 October 2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-362

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in the Linux kernel. A race condition exists in the `xfrm` policy handling, specifically within the `xfrm_policy_bysel_ctx()` function. This flaw allows for a use-after-free vulnerability, where memory is accessed after it has been released. This can lead to system instability or a denial of service (DoS), making the system unresponsive or causing it to crash.

Source: suse_csaf, siemens_advisory, Debian LTS Advisories, Ubuntu Security Notices, redhat_csaf, BSI WID Portal, BSI CSAF, cvelistv5, NVD (NIST), Microsoft Security Update Guide, CVE.org (MITRE)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Linux	Linux	`6.7 – < 6.12.94` `6.13 – < 6.18.36` `5.11 – < 5.15.210` `5.0 – < 5.10.259` `—` `5.16 – < 6.1.176` `6.19 – < 7.0.13` `6.2 – < 6.6.143`	`6.12.94` `6.18.36` `5.15.210` `5.10.259` `7.1` `6.1.176` `7.0.13` `6.6.143`
Siemens	SIMATIC S7	`1500 TM MFP V1.1.1 GNU/Linux subsystem`	—

Vendors and products

Affected operating systems

Affected operating systems

Linux	debian	linux	`bookworm`
Linux	debian	linux	`bullseye`
Linux	debian	linux-6.1	`bullseye`
Linux	linux	linux_kernel	`7.1`
Linux	linux	linux_kernel	—

Weakness classes (CWE)

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Class
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.
Entry at MITRE CWE-362

References & sources

git.kernel.orgstable/c/8fc536e9f6856230f19c7d13e71af064b6a77b22Patch
git.kernel.orgstable/c/c4c1ea36d83bf3c4569468ca5b8b614fda1bf821Patch
git.kernel.orgstable/c/25c8c7fb3b0b9668c7d05e209f58c158d2b020c7Patch
git.kernel.orgstable/c/42827d03f8009a6a218bacab153e21f39d6a121cPatch
git.kernel.orgstable/c/88697cf980222d5906a37bf47662dac0732e2a0fPatch
git.kernel.orgstable/c/b5316e2b8614a87d8736941972441cb47bfd4491Patch
git.kernel.orgstable/c/ec82ea4eb220164d854f8734ca5a35e23e577b94Patch
git.kernel.orgstable/c/7f2d76c9c03257c0782afef9d95321fa04096f60Patch
Siemens ProductCERTproductcert/html/ssa-019113.html
Siemens ProductCERTproductcert/html/ssa-457936.html
Siemens ProductCERTproductcert/html/ssa-784472.html

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

19.10.2026Record modifiedCISA ADP
Weakness type: CWE-362
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Weakness type (CWE) added
—
CWE-362
Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

Individual changes of this event as published by NVD
Type	Action	Before	After
Weakness type (CWE)	added	—	CWE-362

16.10.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2026-53239","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:27:30.875032Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

15.10.2026Record modifiedSiemens ADP

New references:

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/53xxx/CVE-2026-53239.json">CVE-2026-53239</a>
Reference	added	—	https://cert-portal.siemens.com/productcert/html/ssa-457936.html
Reference	added	—	https://cert-portal.siemens.com/productcert/html/ssa-784472.html

Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e

08.09.2026Record modifiedLinux

New references:

and 4 more references

Show 24 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://git.kernel.org/stable/c/25c8c7fb3b0b9668c7d05e209f58c158d2b020c7
Reference	added	—	https://git.kernel.org/stable/c/42827d03f8009a6a218bacab153e21f39d6a121c
Reference	added	—	https://git.kernel.org/stable/c/7f2d76c9c03257c0782afef9d95321fa04096f60
Reference	added	—	https://git.kernel.org/stable/c/88697cf980222d5906a37bf47662dac0732e2a0f
Reference	added	—	https://git.kernel.org/stable/c/8fc536e9f6856230f19c7d13e71af064b6a77b22
Reference	added	—	https://git.kernel.org/stable/c/b5316e2b8614a87d8736941972441cb47bfd4491
Reference	added	—	https://git.kernel.org/stable/c/c4c1ea36d83bf3c4569468ca5b8b614fda1bf821
Reference	added	—	https://git.kernel.org/stable/c/ec82ea4eb220164d854f8734ca5a35e23e577b94
Reference	removed	https://git.kernel.org/stable/c/25c8c7fb3b0b9668c7d05e209f58c158d2b020c7	—
Reference	removed	https://git.kernel.org/stable/c/42827d03f8009a6a218bacab153e21f39d6a121c	—
Reference	removed	https://git.kernel.org/stable/c/7f2d76c9c03257c0782afef9d95321fa04096f60	—
Reference	removed	https://git.kernel.org/stable/c/88697cf980222d5906a37bf47662dac0732e2a0f	—
Reference	removed	https://git.kernel.org/stable/c/8fc536e9f6856230f19c7d13e71af064b6a77b22	—
Reference	removed	https://git.kernel.org/stable/c/b5316e2b8614a87d8736941972441cb47bfd4491	—
Reference	removed	https://git.kernel.org/stable/c/c4c1ea36d83bf3c4569468ca5b8b614fda1bf821	—
Reference	removed	https://git.kernel.org/stable/c/ec82ea4eb220164d854f8734ca5a35e23e577b94	—
Reference type	removed	https://git.kernel.org/stable/c/25c8c7fb3b0b9668c7d05e209f58c158d2b020c7 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/42827d03f8009a6a218bacab153e21f39d6a121c Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/7f2d76c9c03257c0782afef9d95321fa04096f60 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/88697cf980222d5906a37bf47662dac0732e2a0f Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/8fc536e9f6856230f19c7d13e71af064b6a77b22 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/b5316e2b8614a87d8736941972441cb47bfd4491 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/c4c1ea36d83bf3c4569468ca5b8b614fda1bf821 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/ec82ea4eb220164d854f8734ca5a35e23e577b94 Types: Patch	—

Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

08.09.2026Record modifiedSiemens ADP

New references:

https://cert-portal.siemens.com/productcert/html/ssa-019113.html

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/53xxx/CVE-2026-53239.json">CVE-2026-53239</a>
Reference	added	—	https://cert-portal.siemens.com/productcert/html/ssa-019113.html

Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e

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