VulnerabilityPublished 27 Feb 2025Updated 3 Nov 2025

CVE-2025-21792: Linux kernel · ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt

Source GCVE Database

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Not known to be exploited · CVSS 5.5 Medium.

Data as of 30 Oct 2026, 01:13 UTC

CVSS 3.1 base score

5.5Medium

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

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

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
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: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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 27 Feb 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 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.

ghsa-pw8p-q2m4-9ch4

What to do

AI-suggested

A fix for this vulnerability is available in the Linux kernel source code as described in the commit that corrected the reference count handling in ax25_setsockopt(). Users and administrators should update to a kernel version that includes this fix. Since this is a kernel-level issue, applying the official kernel patch or upgrading to a fixed kernel release is the recommended remediation.

Description

CVE-2025-21792 is a vulnerability in the Linux kernel's AX25 protocol implementation where a reference count leak occurs when binding an AX25 device to a socket using the SO_BINDTODEVICE socket option. This leak happens because the reference count increment is missing in this code path, leading to improper resource management and potential memory leaks. The issue was identified and fixed by ensuring that reference counts are correctly incremented and decremented when devices are bound or unbound from sockets.

Impact

This vulnerability leads to a reference count leak in the AX25 protocol implementation, which can cause memory leaks and potentially degrade system stability or availability over time. The CVSS score is 5.5 (medium severity) with an impact primarily on availability (denial of service through resource exhaustion). There is no impact on confidentiality or integrity.

Summary

The Linux kernel AX25 subsystem had a refcount leak triggered by setting the SO_BINDTODEVICE socket option. While the ax25_bind() function correctly increments device reference counts, the ax25_setsockopt() implementation for SO_BINDTODEVICE did not increment the refcount, causing a leak when ax25_release() decrements it. This was reported by Syzkaller through a warning triggered by refcount saturation. The fix involved modifying ax25_setsockopt() to increment the refcount for the newly bound device and decrement it for the previously bound device, ensuring proper lifecycle management of device references.

References

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