Critical Kernel Vulnerability in Linux Package: Memory Management Race Condition
Summary
DEBIAN-CVE-2025-21984: In the Linux kernel, the following vulnerability has been resolved: mm: fix kernel BUG when userfaultfd_move encounters swapcache userfaultfd_move() checks whether the PTE entry is present or a swap entry. Affects linux versions < 6.12.20-1. Fixed in 6.12.20-1. How to fix ↓
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Background
The Linux kernel is the core component of many operating systems, managing hardware resources and providing essential services for applications. It is known for its performance, scalability, and security features. However, vulnerabilities can arise due to complex interactions within its memory management subsystem, as seen in this case.
Vulnerability Detail
In the Linux kernel, a vulnerability has been identified in the memory management subsystem related to the userfaultfd_move function. This issue arises when the function encounters a swap entry that references a folio still present in the swap cache. A race condition can occur between the conversion of PTEs to swap entries and the clearing of the swap cache, leading to potential kernel crashes or unexpected behavior. If KSM is disabled, this can trigger a kernel BUG during the add_rmap operation, resulting in system instability.
How To Fix
Minimum fixed version
6.12.20-1
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 is available.
Conclusion
The identified vulnerability in the Linux kernel poses significant risks to system stability and security. It is crucial for users to update to the patched version to mitigate these risks. Utilizing tools like Vulert can help in monitoring and managing vulnerabilities effectively.
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FAQ
The vulnerability is a race condition in the Linux kernel's memory management that can lead to kernel crashes.
You can use Vulert to monitor and alert for open-source vulnerabilities in your software without requiring access to the code or installation.
Exploitation of this vulnerability can lead to system instability, crashes, and unexpected behavior in applications relying on the kernel.
Yes, a patch has been released in version 6.12.20-1 of the Linux package.
You can use the Vulert playground to check if your application is affected by this vulnerability without any signup.
References
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