Overview
CVE-2025-40216 describes a vulnerability in the Linux kernel related to the io_uring subsystem. Specifically, it addresses an issue where the kernel incorrectly assumed a guaranteed alignment for user-provided virtual addresses. This could lead to unexpected behavior or potential security implications.
This vulnerability has been resolved in recent kernel updates. This blog post will detail the technical aspects of the vulnerability, its potential impact, and the necessary mitigation steps.
Technical Details
The io_uring subsystem in the Linux kernel is designed for high-performance asynchronous I/O operations. The vulnerability arises from how the kernel calculates an offset into a folio (a unit of memory management), after coalescing data. The problematic code relied on specific bitmask logic that assumed a certain alignment of user-supplied virtual addresses. Because there’s no guarantee on user-provided memory alignment, this assumption could be violated, leading to incorrect offset calculations.
The fix involves removing the problematic bitmask logic and ensuring proper handling of user-provided addresses regardless of their alignment.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) score for CVE-2025-40216 is currently listed as N/A. This is likely because the direct impact of the vulnerability might not be immediately exploitable for arbitrary code execution or other critical security breaches. However, incorrect memory handling can lead to instability or denial-of-service conditions. A CVSS score might be assigned later based on further analysis of the vulnerability’s full potential.
Severity: N/A
Possible Impact
While the CVSS score is N/A, the vulnerability could potentially lead to the following:
- Kernel Instability: Incorrect memory offset calculations could cause unexpected behavior within the kernel, leading to crashes or other forms of instability.
- Denial of Service (DoS): A carefully crafted request leveraging this vulnerability might be able to trigger a kernel panic or other denial-of-service conditions.
- Information Leakage (Potentially): Although less likely, it’s possible that the incorrect offset calculation could, in some scenarios, lead to the leakage of sensitive kernel information.
Mitigation or Patch Steps
The vulnerability has been addressed in the upstream Linux kernel. The primary mitigation step is to update your kernel to a version that includes the fix. Specifically, look for kernels containing the following commits (or later):
- Commit 1: 3a3c6d61577dbb23c09df3e21f6f9eda1ecd634b
- Commit 2: 50998b0ae7d9d552e96d8b7239981cf05f65eff5
- Commit 3: f16769241594be59387b56ab525e327f54377e60
Most Linux distributions will provide patched kernel versions through their standard update mechanisms. Ensure your system is configured to receive security updates and apply them promptly.
References
https://git.kernel.org/stable/c/3a3c6d61577dbb23c09df3e21f6f9eda1ecd634b
https://git.kernel.org/stable/c/50998b0ae7d9d552e96d8b7239981cf05f65eff5
https://git.kernel.org/stable/c/f16769241594be59387b56ab525e327f54377e60
