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.

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History

Tue, 09 Jun 2026 15:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-250
CWE-269

Tue, 09 Jun 2026 13:30:00 +0000

Type Values Removed Values Added
Description 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.
Title 9p: fix access mode flags being ORed instead of replaced
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
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cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-06-09T12:36:03.521Z

Reserved: 2026-06-09T07:44:35.366Z

Link: CVE-2026-52906

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-06-09T14:16:45.047

Modified: 2026-06-09T14:16:45.047

Link: CVE-2026-52906

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-06-09T15:00:07Z

Weaknesses