GHSA-4VM9-M655-VQF4
Vulnerability from github – Published: 2026-06-09 15:32 – Updated: 2026-06-14 06:30In 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.
{
"affected": [],
"aliases": [
"CVE-2026-52906"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-06-09T14:16:45Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: fix access mode flags being ORed instead of replaced\n\nSince commit 1f3e4142c0eb (\"9p: convert to the new mount API\"),\nv9fs_apply_options() applies parsed mount flags with |= onto flags\nalready set by v9fs_session_init(). For 9P2000.L, session_init sets\nV9FS_ACCESS_CLIENT as the default, so when the user mounts with\n\"access=user\", both bits end up set. Access mode checks compare\nagainst exact values, so having both bits set matches neither mode.\n\nThis causes v9fs_fid_lookup() to fall through to the default switch\ncase, using INVALID_UID (nobody/65534) instead of current_fsuid()\nfor all fid lookups. Root is then unable to chown or perform other\nprivileged operations.\n\nFix by clearing the access mask before applying the user\u0027s choice.",
"id": "GHSA-4vm9-m655-vqf4",
"modified": "2026-06-14T06:30:24Z",
"published": "2026-06-09T15:32:19Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-52906"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
]
}
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