In the Linux kernel, a vulnerability has been discovered pertaining to the io_uring/eventfd functionality. The issue arises when the io_eventfd_signal() function is invoked from an RCU callback. The direct invocation of io_eventfd_free() when the reference count drops to zero is incorrect, as any potential freeing of the io_ev_fd should be deferred for another RCU grace period. The correct approach is to call io_eventfd_put() to ensure proper deferral.
This vulnerability has been classified with a CVSS score of 4.7, indicating its medium severity. This rating is significant as it highlights the potential impact of the vulnerability, which affects the availability of systems running certain versions of the Linux kernel.
Currently, this vulnerability does not have any known exploits, and it is not listed in the Known Exploited Vulnerabilities (KEV) catalog. However, the potential for availability impact necessitates that organizations take proactive measures to address it.
Organizations should prioritize patching immediately to mitigate risks associated with this vulnerability. Given the potential impacts, ensuring systems are updated is critical in maintaining operational integrity.
Vulnerability Details
The Linux kernel vulnerability CVE-2025-21655 is characterized by an issue in the io_uring/eventfd component. The vulnerability allows for improper handling of references to io_ev_fd, which can lead to availability issues. The CVSS vector for this vulnerability is CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H, defining the attack vector as local, with a high attack complexity, and low privileges required.
Affected versions of the Linux kernel include version ranges from 6.1 to 6.1.125, 6.2 to 6.6.72, and 6.7 to 6.12.10. Additionally, specific release candidates of version 6.13 are also affected.
The vulnerability falls under CWE-416, which relates to use-after-free issues. It is essential for organizations to be aware of these details to understand the potential impacts on their systems.
Technical Analysis
The root cause of the vulnerability stems from improper reference handling in the io_eventfd_do_signal() function. Invoked from an RCU callback, the function directly frees the io_ev_fd when the reference count drops to zero, which is not the appropriate behavior. Instead, freeing should be deferred until after another RCU grace period to prevent premature deallocation.
The attack vector is classified as local, indicating that an attacker would need local access to exploit this vulnerability. The complexity of an attack is rated as high due to the requirement of specific conditions being met, including the state of the reference count.
No user interaction is required to exploit the vulnerability, and it has a low privilege requirement, meaning that an attacker with limited access could potentially exploit the flaw.
The impact of the vulnerability is significant with regards to availability, as the improper handling of references can lead to system instability or crashes if exploited. There are no confidentiality or integrity impacts reported.
Risk & Impact Analysis
Risk to organizations includes potential service disruptions or crashes due to the availability impact of this vulnerability. With a medium severity rating, the exploitation risk is present, although currently, there are no confirmed public exploits. Organizations should consider the real-world impact based on their specific use cases and deployment environments.
Given the CVSS score of 4.7, organizations should assess their risk management strategies. Although the vulnerability is not actively exploited in the wild, the potential for availability issues necessitates immediate attention.
Organizations should address this vulnerability in their priority patch cycle to mitigate any potential risks associated with it. The availability impact could have a significant blast radius, particularly for systems relying heavily on the Linux kernel.
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions of the Linux kernel include:
- 6.1 to 6.1.125, 6.2 to 6.6.72, 6.7 to 6.12.10, and specific release candidates 6.13:rc1 to 6.13:rc6.
Mitigation & Remediation
To mitigate the risk associated with CVE-2025-21655, organizations must apply the necessary patches provided by the Linux kernel maintainers. Information regarding the patches can be found in the kernel's official repositories.
Organizations should prioritize patching immediately to remediate this vulnerability. In the absence of immediate patch availability, organizations may consider implementing workarounds or configuration hardening to reduce exposure.
Monitoring for unusual behavior and ensuring that systems are correctly configured can also serve as temporary mitigations until a patch is applied. For more information on effective patching strategies, organizations can refer to penetration testing methodology.
Detection Guidance
Security teams should monitor logs for indicators related to the io_uring/eventfd functionality and watch for any abnormal behavior that could suggest exploitation attempts. Additionally, ensuring that systems have the latest security patches can assist in detecting any vulnerabilities proactively.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-21655 lies in its representation of ongoing challenges in reference management in local execution contexts. Security teams should learn from this incident to reinforce their defensive strategies against similar vulnerabilities.
As organizations integrate increasingly complex kernel functionalities, ensuring robust testing and validation processes becomes paramount. This incident serves as a reminder of the intricate nature of kernel programming and the potential for critical vulnerabilities to arise.
For further insights into vulnerability management, organizations may refer to vulnerability management program design and best practices for security testing.
Organizations should also consider the implications of this vulnerability on their overall security posture and engage in continuous security assessments, such as continuous penetration testing to identify and address similar weaknesses.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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