9p: fix access mode flags being ORed instead of replaced

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Summary

CVECVE-2026-52906
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-09 14:16:45 UTC
Updated2026-07-08 21:44:36 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.7 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS: 0.001210000 probability, percentile 0.022180000 (date 2026-07-08)

Problem Types: NVD-CWE-noinfo

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.7HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED7.7HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1f3e4142c0eb178089ea0cbc97506a061470ad27 b8f037e87a083291190204b959cda417aaf01058 git Not specified
CNA Linux Linux affected 1f3e4142c0eb178089ea0cbc97506a061470ad27 da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9 git Not specified
CNA Linux Linux affected 6.19 Not specified
CNA Linux Linux unaffected 6.19 semver Not specified
CNA Linux Linux unaffected 7.0.4 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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