FKIE_CVE-2026-52906

Vulnerability from fkie_nvd - Published: 2026-06-09 14:16 - Updated: 2026-06-09 14:16
Severity
Summary
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9
Impacted products
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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": "CVE-2026-52906",
  "lastModified": "2026-06-09T14:16:45.047",
  "metrics": {},
  "published": "2026-06-09T14:16:45.047",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}


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