CVE-2025-21756VulnerabilityPublished 21 May 2025Updated 27 Jun 2026

Red Hat Security Advisory: kernel security update

Affects Red HatSource GCVE Database

Not known to be exploited : upgrade to 9.4.1 soon.

Data as of 25 Oct 2026, 19:02 UTC

Severity

High

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

EPSS: 0.8% chance of exploitation in 30 days – higher than 59% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 9.4.1

Exploitation evidence

Disclosed: evidence found.
CVE published 21 May 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 2026-10-25.

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

Upgrade redhat/kernel to 9.4.1.

Affected software

Product	Affected	Fixed in
Red Hatredhat/kernel`pkg:rpm/redhat/kernel`Other threats	Affected =9.4 <9.4.1	Fixed in 9.4.1

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

AI-suggested

Red Hat has released an official security update for Red Hat Enterprise Linux 9.4 Extended Update Support that addresses CVE-2025-21756. Users should apply the kernel update as described in Red Hat advisory RHSA-2025:8058 and reboot affected systems to activate the fix. No additional mitigation steps are indicated by the vendor.

Description

The kernel packages contain the Linux kernel, the core of any Linux operating system. Security Fix(es): * kernel: vsock: Keep the binding until socket destruction (CVE-2025-21756) 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 vulnerability affects the Linux kernel's vsock subsystem, which could lead to use-after-free conditions. This may allow an attacker to cause system instability or potentially execute arbitrary code, depending on exploitation. However, no known exploits have been reported in the wild. The impact is rated as Important by Red Hat, indicating a significant security concern that warrants prompt patching.

Summary

CVE-2025-21756 is a vulnerability in the Linux kernel's vsock component where the binding is not kept until socket destruction, potentially leading to use-after-free conditions (CWE-416). Red Hat has issued a security advisory (RHSA-2025:8058) providing an update for Red Hat Enterprise Linux 9.4 Extended Update Support to fix this issue. The advisory instructs users to apply the kernel update and reboot the system to ensure the fix is applied. The vulnerability is rated as Important by Red Hat and high severity by the source, but no CVSS score is provided. No exploits are currently known in the wild.

CWE-416Use After Free (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #7
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Architecture and Design · Language Selection
Choose a language that provides automatic memory management.
Implementation · Attack Surface Reduction
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).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Jun 2026, 22:09 UTC

WeaknessesCWE-416

Technical details

References

Community reviews

Related threats