Off-by-One Error in Linux Kernel Timers Migration - CVE-2025-21813
Summary
DEBIAN-CVE-2025-21813: In the Linux kernel, the following vulnerability has been resolved: timers/migration: Fix off-by-one root mis-connection Before attaching a new root to the old root, the children counter of the new root is checked to ver... Affects linux versions < 6.12.15-1. Fixed in 6.12.15-1. How to fix ↓
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Background
The Linux kernel is the core component of many operating systems, responsible for managing hardware resources and providing essential services to software applications. It is known for its robustness and flexibility, supporting a wide range of hardware architectures. However, vulnerabilities can arise due to complex interactions within its subsystems, such as the timers migration feature, which is crucial for managing CPU idle states and task scheduling.
Vulnerability Detail
The vulnerability identified as CVE-2025-21813 is an off-by-one error in the Linux kernel's timers migration functionality. This issue stems from a recent commit that altered the way the kernel checks the children count of a new root before attaching it to an old root. The faulty logic allows the system to potentially operate with multiple top-level roots, undermining the intended single idle migrator design. This could lead to unpredictable system behavior, including performance degradation and instability, as the kernel may mismanage CPU resources.
How To Fix
Minimum fixed version
6.12.15-1
This is the first release that contains the fix.
sudo apt-get install --only-upgrade linuxTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
Currently, there are no specific workarounds mentioned for this vulnerability. It is recommended to apply the patch as soon as it becomes available to mitigate any risks associated with the vulnerability.
Conclusion
CVE-2025-21813 represents a significant vulnerability in the Linux kernel that could lead to system instability due to improper handling of timers migration. Users are strongly advised to update to the patched version to mitigate risks associated with this issue.
See every vulnerability recorded for linux →
FAQ
CVE-2025-21813 is a vulnerability in the Linux kernel related to an off-by-one error in the timers migration feature, which could lead to multiple top-level roots being created.
This vulnerability can lead to unpredictable behavior and performance degradation as the kernel may mismanage CPU resources due to the incorrect handling of root connections.
You should update your Linux kernel to version 6.12.15-1 or later to ensure that the vulnerability is patched.
Yes, you can use Vulert, which monitors open-source vulnerabilities in your software by analyzing a manifest file like package-lock.json. You can check for vulnerabilities in your application using the Vulert playground without any signup.
Failing to address this vulnerability could result in system instability, performance issues, and increased risk of exploitation by malicious actors.
References
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