In the Linux kernel, a new vulnerability has been identified regarding the handling of CPU scheduling. The vulnerability arises from the use of the rq_lock() function in the scx_ops_bypass() method, which iterates over all CPUs to re-enqueue scx tasks. The rq_lock() function is meant for online CPUs, and its incorrect usage can trigger unnecessary warnings when CPUs are offline or running higher-priority tasks. Specifically, it has been recommended to replace rq_lock() with raw_spin_rq_lock() to prevent these warnings and ensure proper functionality.
This vulnerability is classified with a CVSS score of 5.5, indicating medium severity. Such vulnerabilities pose a risk to organizations, particularly in environments where the Linux kernel is utilized for critical operations. The potential impact includes high availability issues, as the incorrect handling can lead to system warnings and degraded performance.
As of now, there are no known exploits or proof of concepts publicly available for this vulnerability, which is a positive indicator for organizations. However, the urgency for patching remains high due to the potential risks involved in kernel-level vulnerabilities.
Organizations should prioritize patching immediately to mitigate any risks associated with this vulnerability. Keeping systems up-to-date with the latest patches is essential for maintaining security and stability.
Vulnerability Details
The vulnerability described in CVE-2025-21657 pertains to the Linux kernel's scheduling functions. The official description indicates that the method scx_ops_bypass() incorrectly uses rq_lock() for locking, which can lead to warnings in the system logs, impacting system reliability.
The CVSS score of 5.5 reflects a medium severity level, with the vulnerability classified under the following metrics: attack vector (local), attack complexity (low), privileges required (low), and no user interaction required. This indicates that an attacker with low privileges could potentially exploit this vulnerability under certain conditions.
The Linux kernel versions affected include those from 6.12.1 to 6.12.9, as well as various release candidates in the 6.13 series. This places a significant number of systems at risk if they are running these versions.
Technical Analysis
The root cause of this vulnerability stems from the misuse of locking mechanisms within the Linux kernel. The scx_ops_bypass() function's design requires iterating over all CPUs to manage task scheduling, and the reliance on rq_lock() for locking introduces potential issues when CPUs are offline or under different scheduling conditions.
The attack vector for this vulnerability is classified as local, meaning that an attacker would need local access to the system to exploit it. The complexity of the attack is low, and the privileges required are also low, making it easier for an attacker with minimal access to potentially exploit the system.
No user interaction is required for this vulnerability to be exploited, which adds to the risk profile. The impacts on confidentiality and integrity are none, but the availability impact is rated as high, indicating that system performance could degrade significantly due to the warnings generated by the incorrect locking.
Risk & Impact Analysis
The real-world deployment risk associated with CVE-2025-21657 is significant, particularly for organizations relying on the Linux kernel for critical operations. The potential for high availability issues means that affected systems could experience performance degradation, leading to operational disruptions.
Organizations should consider the broader implications of this vulnerability, as the blast radius could extend to any systems running the affected kernel versions. Given the widespread use of Linux in various environments, the urgency for remediation is critical.
The CVSS score of 5.5 suggests that this vulnerability should be addressed in a priority patch cycle. Organizations should evaluate their current systems to identify any installations that may be running vulnerable versions and plan for immediate remediation.
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The following versions of the Linux kernel are affected by this vulnerability: 6.12.1 through 6.12.9, as well as various release candidates in the 6.13 series. Organizations running these versions should take immediate action to address the vulnerability.
Mitigation & Remediation
Organizations should ensure they are running the latest patched version of the Linux kernel. The patches addressing CVE-2025-21657 are available and should be applied as soon as possible to prevent potential availability issues. If immediate patching is not feasible, consider implementing configuration hardening and network controls to mitigate risks.
For further details on security assessments, organizations can refer to the relevant resources on application security assessments and explore options for continuous security testing.
Detection Guidance
Organizations should monitor system logs for any unusual warnings or error messages related to task scheduling. Behavioral anomalies, such as unexpected CPU load or performance degradation, should also be investigated. Implementing network signatures that flag unusual CPU task management operations can provide additional layers of detection.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-21657 lies in its potential impact on the stability of systems utilizing the Linux kernel. The trend towards kernel-level vulnerabilities underscores the need for ongoing vigilance and proactive security measures. Security teams are encouraged to learn from such vulnerabilities and adopt a comprehensive strategy for securing their systems.
For further insights on vulnerability management and effective remediation strategies, organizations can refer to the vulnerability management program and explore the best practices outlined in the penetration testing methodology guide to enhance security posture.
Organizations should also consider continuous security testing, leveraging services such as continuous penetration testing to identify and remediate similar vulnerabilities promptly.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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