CVE-2025-39964VulnerabilityPublished 24 Sep 2026Updated 29 Oct 2026

Red Hat Security Advisory: kernel security update

Affects Linux kernelSource GCVE Database

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Mentioned vulnerabilities

CVE-2026-53266

Exploited in the wild · KEV due 21 Sep 2026 · 1% EPSS : apply the vendor's fix or mitigations to Linux kernel now.

Data as of 29 Oct 2026, 07:27 UTC

Exploitation

Actively exploited

High severity · CVSS not yet scored by NVD

KEV deadline: 21 Sep 2026 US federal agencies must patch by this date; a sensible deadline for everyone else. Other KEV due dates
EPSS: 1.5% chance of exploitation in 30 days – higher than 75% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 24 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
Exploited in the wildExploited: evidence found.
Listed in CISA KEV 6 days before disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

Added to CISA KEV (opens in a new tab)
exploitation confirmed
18 Sep 2026, 6 days before disclosure
KEV remediation due
US federal deadline
21 Sep 2026, 3 days before disclosure
CVE published
on cve.org
24 Sep 202606:26 UTC, t = 0

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), GitHub proofs of concept, CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Description

Red Hat has issued a security advisory for the Linux kernel packages addressing two vulnerabilities: CVE-2025-39964 and CVE-2026-53266. The first vulnerability involves disallowing concurrent writes in the af_alg_sendmsg function of the crypto subsystem. The second involves the ebtables SNAT target writing to shared memory pages during ARP hardware address rewrite in the netfilter subsystem. These vulnerabilities affect Red Hat Enterprise Linux 10.0 Extended Update Support and related CodeReady Linux Builder products. A kernel update is available that addresses these issues, and a system reboot is required to apply the update. Red Hat rates the update as important and advises prompt installation to improve security posture. Exploitation in the wild is known for these vulnerabilities.

Impact

The vulnerabilities affect the Linux kernel's core components, potentially allowing unsafe concurrent writes in the crypto subsystem and unsafe memory writes in the netfilter subsystem. These issues could lead to system instability or security breaches. Given the kernel's fundamental role, any flaw can have significant security implications. Exploits for these vulnerabilities are known to exist in the wild, increasing the urgency for remediation. The advisory rates the security impact as important, indicating a high risk to affected systems if unpatched.

Mitigation

Red Hat has released updated kernel packages that fix these vulnerabilities. Users should apply the kernel update as provided in the advisory and reboot their systems to ensure the fixes take effect. Red Hat strongly recommends treating all kernel errata as security-relevant and advises against delaying updates to avoid exposure. Detailed update instructions are available at https://access.redhat.com/articles/11258. No additional mitigations are specified beyond applying the official update and rebooting.

CWE-366Race Condition within a Thread (opens in a new tab)
Base weaknessLikelihood of exploit: Medium
If two threads of execution use a resource simultaneously, there exists the possibility that resources may be used while invalid, in turn making the state of execution undefined.
Architecture and Design
Use locking functionality. This is the recommended solution. Implement some form of locking mechanism around code which alters or reads persistent data in a multithreaded environment.
Architecture and Design
Create resource-locking validation checks. If no inherent locking mechanisms exist, use flags and signals to enforce your own blocking scheme when resources are being used by other threads of execution.
OWASP Cheat Sheets
Abuse Case (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).
CWE-825Expired Pointer Dereference (opens in a new tab)
Base weakness
The product dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid.
Architecture and Design
Choose a language that provides automatic memory management.
Implementation
When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-362Concurrent Execution using Shared Resource with Improper Synchronization (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

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Exploitation evidence

Timeline

What to do

Description

AI analysisMachine-generated, updated 29 Oct 2026, 07:27 UTC

Public exploits and detectionGitHub proofs of concept

WeaknessesCWE-366, CWE-825, CWE-362

Technical details

References

Community reviews

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