CVE-2025-39825VulnerabilityPublished 17 Dec 2025Updated 30 Jul 2026

Red Hat Security Advisory: kernel security update

Affects Red HatSource GCVE Database

Mentioned vulnerabilities

Not known to be exploited.

Data as of 26 Oct 2026, 08:30 UTC

Severity

High

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.1% chance of exploitation in 30 days – higher than 1% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Dec 2025
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 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

Affected software

Product	Affected	Fixed in
Red Hatredhat/kernel`pkg:rpm/redhat/kernel`Other threats	Affected =4.18.0-372.173.1.el8_6	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A security update for the kernel packages is available from Red Hat for Red Hat Enterprise Linux 8.6 variants. Applying the update and rebooting the system is required to remediate these vulnerabilities. Refer to Red Hat's official advisory RHSA-2025:23425 and article https://access.redhat.com/articles/11258 for detailed update instructions. No additional mitigation steps are indicated beyond applying the official patch and rebooting.

Description

The kernel packages contain the Linux kernel, the core of any Linux operating system. Security Fix(es): * kernel: smb: client: fix race with concurrent opens in rename(2) (CVE-2025-39825) * kernel: tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect() (CVE-2025-39955) * kernel: tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request() (CVE-2025-40186) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Impact

The vulnerabilities impact the Linux kernel's SMB client and TCP networking stack, potentially leading to race conditions and improper TCP socket state management. This could affect system stability or security in scenarios involving concurrent file operations over SMB and TCP connection handling. The advisory rates the impact as important/high severity but does not specify exact exploitation details or CVSS scores. No known exploits in the wild have been reported at this time.

Summary

This Red Hat security advisory (RHSA-2025:23425) addresses three kernel vulnerabilities in Red Hat Enterprise Linux 8.6. CVE-2025-39825 fixes a race condition in the SMB client related to concurrent file opens during the rename(2) system call. CVE-2025-39955 and CVE-2025-40186 address TCP stack issues involving the handling of tcp_sk(sk)->fastopen_rsk in tcp_disconnect() and the improper invocation of reqsk_fastopen_remove() in tcp_conn_request(), respectively. These fixes prevent potential kernel-level race conditions and improper TCP socket state handling. The advisory requires applying updated kernel packages and rebooting the system for the fixes to take effect.

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-213Exposure of Sensitive Information Due to Incompatible Policies (opens in a new tab)
Base weaknessOWASP Top 10 A04:2021: Insecure Design (opens in a new tab)
The product's intended functionality exposes information to certain actors in accordance with the developer's security policy, but this information is regarded as sensitive according to the intended security policies of other stakeholders such as the product's administrator, users, or others whose information is being processed.
OWASP Cheat Sheets
Error Handling (opens in a new tab)
Logging (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.4 (opens in a new tab)
V14.3.3 (opens in a new tab)
V7.3.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-826Premature Release of Resource During Expected Lifetime (opens in a new tab)
Base weakness
The product releases a resource that is still intended to be used by itself or another actor.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Jun 2026, 22:16 UTC

WeaknessesCWE-366, CWE-213, CWE-826

Technical details

References

Community reviews

Related threats