VulnerabilityPublished 27 Feb 2025Updated 3 Nov 2025

CVE-2025-21823: Linux kernel · batman-adv: Drop unmanaged ELP metric worker

Source GCVE Database

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Not known to be exploited · CVSS 5.5 Medium.

Data as of 30 Oct 2026, 01:14 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-cq4r-9fv8-53r2

What to do

AI-suggested

A fix has been implemented in the Linux kernel batman-adv module that removes the per-interface neighbor metric worker and consolidates metric gathering to avoid deadlocks and invalid memory accesses. Users should update to the fixed kernel version once available. Until patched, avoid unloading the batman-adv module or removing interfaces abruptly if possible to reduce risk.

Description

CVE-2025-21823 is a medium severity vulnerability in the Linux kernel's batman-adv module related to the handling of the ELP metric worker. The issue arises from the previous design where per-interface neighbor metric workers could continue running even after interfaces were removed or the module unloaded, potentially causing invalid memory accesses. The fix involves removing the per-interface neighbor metric worker and consolidating metric gathering within the interface worker, using RCU locking mechanisms carefully to avoid deadlocks and ensure proper cleanup.

Impact

This vulnerability could lead to invalid memory accesses and potential kernel instability or crashes (denial of service) due to improper cleanup of metric worker tasks when interfaces are removed or the module is unloaded. There is no indication of confidentiality or integrity impact. The CVSS score of 5.5 reflects a medium severity with local attack vector, low complexity, and no user interaction required.

Summary

The vulnerability in batman-adv involved the ELP metric worker calculating metrics for neighbors reachable over an interface. The original design used per-neighbor work items to avoid RCU vs might_sleep() conflicts but lacked proper cancellation of these work items when interfaces were removed or the module unloaded, risking invalid memory access. Attempts to cancel work synchronously caused deadlocks due to rtnl_lock usage. The improved approach eliminates per-interface neighbor metric workers, instead gathering neighbor metrics in a list created within an RCU-protected context and performing metric calculations outside it, using rcu_trylock to avoid deadlocks during interface removal.

References

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