CVE-2026-52906
HighCVSS 7.7Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
In the Linux kernel's 9p filesystem, a vulnerability was found where access mode flags are ORed instead of replaced. When mounting with 'access=user', both V9FS_ACCESS_CLIENT and V9FS_ACCESS_USER flags are set, preventing proper operation of privileged commands like chown.
Risk Assessment
The root user may lose the ability to perform privileged operations on the mounted 9p filesystem, potentially leading to permission management issues.
Recommendation
It is recommended to update the Linux kernel to a version containing the fix for this vulnerability.
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In the Linux kernel XFS filesystem, during directory tree repair, a self-referential directory may be detected. In such a case, the repair code attempts to lock the same inode twice (double iolock/ilock), leading to a deadlock. The fix detects this corner case and handles it appropriately.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: 9p: fix access mode flags being ORed instead of replaced Since commit 1f3e4142c0eb ("9p: convert to the new mount API"), v9fs_apply_options() applies parsed mount flags with |= onto flags already set by v9fs_session_init(). For 9P2000.L, session_init sets V9FS_ACCESS_CLIENT as the default, so when the user mounts with "access=user", both bits end up set. Access mode checks compare against exact values, so having both bits set matches neither mode. This causes v9fs_fid_lookup() to fall through to the default switch case, using INVALID_UID (nobody/65534) instead of current_fsuid() for all fid lookups. Root is then unable to chown or perform other privileged operations. Fix by clearing the access mask before applying the user's choice.

