VDB-292612 · CVE-2025-21655 · Nessus 215034

Linux Kernel up to 6.1.124/6.6.71/6.12.9 eventfd io_eventfd_signal reference count

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4.9	$0-$5k	0.00

Summaryinfo

A vulnerability described as problematic has been identified in Linux Kernel up to 6.1.124/6.6.71/6.12.9. Affected by this issue is the function io_eventfd_signal of the component eventfd. Executing a manipulation can lead to reference count. This vulnerability is tracked as CVE-2025-21655. Moreover, an exploit is present. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.1.124/6.6.71/6.12.9 and classified as problematic. This vulnerability affects the function io_eventfd_signal of the component eventfd. The manipulation with an unknown input leads to a reference count vulnerability. The CWE definition for the vulnerability is CWE-911. The product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. As an impact it is known to affect availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2025-21655 since 12/29/2024. Technical details and also a public exploit are known.

It is possible to download the exploit at 0day.today. It is declared as proof-of-concept. The vulnerability scanner Nessus provides a plugin with the ID 215034 (Amazon Linux 2023 : bpftool, kernel, kernel-devel (ALAS2023-2025-823)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.125, 6.6.72 or 6.12.10 eliminates this vulnerability. Applying the patch 6b63308c28987c6010b1180c72a6db4df6c68033/8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10/a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7/c9a40292a44e78f71258b8522655bffaf5753bdb is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at 0day.today (39928), Tenable (215034) and CERT Bund (WID-SEC-2025-0132). Once again VulDB remains the best source for vulnerability data.

Affected

Open Source Linux Kernel
Debian Linux
Red Hat Enterprise Linux
Ubuntu Linux
SUSE Linux
RESF Rocky Linux
Dell NetWorker

Productinfo

Type

Operating System

Vendor

Linux

Name

Kernel

Version

License

open-source

Website

Vendor: https://www.kernel.org/

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.2
VulDB Meta Temp Score: 4.9

VulDB Base Score: 5.7
VulDB Temp Score: 5.1
VulDB Vector: 🔍
VulDB Reliability: 🔍

NVD Base Score: 4.7
NVD Vector: 🔍

CVSSv2info

AV	AC	Au	C	I	A
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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

Exploitinginfo

Class: Reference count
CWE: CWE-911 / CWE-664
CAPEC: 🔍
ATT&CK: 🔍

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔍
Access: Public
Status: Proof-of-Concept
Download: 🔍

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍