Linux Kernel Vulnerability in fscrypt: Owner Check Bypass in Debian Packages
Summary
DEBIAN-CVE-2026-74595: In the Linux kernel, the following vulnerability has been resolved: fscrypt: use the mount idmap for the owner check in fscrypt_ioctl_set_policy() fscrypt_ioctl_set_policy() calls inode_owner_or_capable() with &nop_mnt_i... Affects linux versions 6.1.106-1 – 7.2~rc7-1~exp1. No fix is published. How to fix ↓
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Background
The Linux kernel is a core component of the Debian operating system, providing essential services for hardware and software interaction. It supports various filesystems, including ext4 and f2fs, which utilize fscrypt for encryption. This vulnerability affects the owner check mechanism in fscrypt, potentially allowing unauthorized access to encrypted files.
Vulnerability Detail
In the Linux kernel, a vulnerability was identified in the fscrypt subsystem, specifically in the fscrypt_ioctl_set_policy() function. This function incorrectly uses a mount idmap for owner checks, leading to a situation where the actual owner of a file can be denied access with an -EACCES error, while an unrelated caller may be granted access. This flaw arises from the function calling inode_owner_or_capable() with &nop_mnt_idmap instead of the correct idmap of the mount where the ioctl was issued. This can result in serious security implications for filesystems that support idmapped mounts.
How To Fix
No fixed version is published for this vulnerability.
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Workaround
As a temporary workaround, users can avoid using idmapped mounts for filesystems that utilize fscrypt until the kernel is updated to a secure version. This may not be feasible for all users, so applying the patch is recommended as the best solution.
Conclusion
The vulnerability in the Linux kernel's fscrypt subsystem poses a serious risk by allowing unauthorized access to encrypted files. Users are strongly advised to update their kernel to the latest patched version to mitigate this risk. Temporary workarounds are available, but applying the patch is the most effective solution.
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FAQ
The vulnerability can allow unauthorized users to access encrypted files, posing a significant security risk.
You can use tools like Vulert to monitor and alert for open-source vulnerabilities in your software. Visit Vulert Scanner to check if your application is affected.
Yes, a patch has been released for the Linux kernel. Updating to the latest version will resolve the issue.
As a temporary measure, avoid using idmapped mounts for filesystems that utilize fscrypt until you can apply the patch.
Detailed information can be found in the Debian security advisories and the official CVE documentation for CVE-2026-74595.
References
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