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CVE-2026-89641 (GCVE-0-2026-89641)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size()
Summary
In the Linux kernel, the following vulnerability has been resolved: cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size() When the else branch of cifs_file_set_size() finds a writable file handle via find_writable_file(), it borrows tcon and server from the handle's tlink, attempts the handle-based set_file_size() RPC, and then releases the handle with cifsFileInfo_put(). If set_file_size() fails, execution falls through to the path-based fallback, which reuses the borrowed tcon and server under the "if (tcon == NULL)" guard. Since tcon is not NULL at that point, the guard is skipped. If cifsFileInfo_put() dropped the last reference on a tlink that was already removed from the tlink tree (TCON_LINK_IN_TREE cleared, as happens during reconnection or session teardown), cifs_put_tlink() will have freed tcon; the subsequent set_path_size() call is then a use-after-free. Setting tcon = NULL after cifsFileInfo_put() causes the existing guard to take the cifs_sb_tlink() path, which acquires a fresh reference for the path-based operation or fails cleanly if the session is gone.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < 4f18c9e7ee464aaae5cd9fccdb943b3fcb4655d4 (git)
Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < 4bea15d9c7683218f57b8c1f5f0aa75cab76af8d (git)
Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < b96db32fed8dfb2478d7c208f89bf383beed1535 (git)
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Linux Linux Affected: 6.18
Unaffected: 0 , < 6.18 (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size()\n\nWhen the else branch of cifs_file_set_size() finds a writable file handle\nvia find_writable_file(), it borrows tcon and server from the handle\u0027s\ntlink, attempts the handle-based set_file_size() RPC, and then releases\nthe handle with cifsFileInfo_put().\n\nIf set_file_size() fails, execution falls through to the path-based\nfallback, which reuses the borrowed tcon and server under the\n\"if (tcon == NULL)\" guard.  Since tcon is not NULL at that point, the\nguard is skipped.  If cifsFileInfo_put() dropped the last reference on a\ntlink that was already removed from the tlink tree (TCON_LINK_IN_TREE\ncleared, as happens during reconnection or session teardown),\ncifs_put_tlink() will have freed tcon; the subsequent set_path_size()\ncall is then a use-after-free.\n\nSetting tcon = NULL after cifsFileInfo_put() causes the existing guard\nto take the cifs_sb_tlink() path, which acquires a fresh reference for\nthe path-based operation or fails cleanly if the session is gone."
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              "value": "AV:L - The UAF is in the CIFS client setattr path (fs/smb/client/inode.c cifs_file_set_size), reached only via local VFS truncate/setattr on a mounted SMB share (sys_truncate \u2192 vfs_truncate \u2192 notify_change \u2192 cifs_setattr), not via ksmbd or unsolicited SMB receive processing.\nAC:L - A local attacker controls both sides: keep a writable handle open, issue truncate(2) to hit the find_writable_file() else branch, fail handle-based set_file_size (controlled/malicious server or reconnect), and concurrently umount/teardown so TCON_LINK_IN_TREE is already cleared when cifsFileInfo_put() drops the last tlink ref.\nPR:L - Any unprivileged user with write access on an existing CIFS mount can invoke truncate(2); vfs_truncate only requires MAY_WRITE and setattr_prepare does not demand CAP_SYS_ADMIN. CIFS is not FS_USERNS_MOUNT, but the vulnerable path itself needs no init-namespace capability.\nUI:N - The attacker performs open/truncate (and optional umount) themselves on a reachable CIFS mount such as an enterprise automount or a share they mounted; no separate victim action is required at exploit time.\nS:U - This is a standard in-kernel heap use-after-free of struct cifs_tcon on the client host, enabling privilege escalation within the same kernel security authority and not a VM, IOMMU, or sandbox escape.\nC:H - After cifsFileInfo_put() can free tcon, set_path_size()/smb2_compound_op() reads the freed cifs_tcon; kernel UAF of this heap object enables reuse/spraying and arbitrary kernel memory disclosure.\nI:H - The same freed tcon is passed into SMB2 compound operations that write tcon fields and follow tcon-\u003eses pointers, so heap spraying yields arbitrary write and potential control-flow hijack primitives.\nA:H - Use-after-free of tcon in the path-based set_path_size fallback causes kernel oops/panic even without full exploitation, fully denying availability."
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    "cveId": "CVE-2026-89641",
    "datePublished": "2026-09-11T19:45:34.036Z",
    "dateReserved": "2026-09-11T19:38:34.740Z",
    "dateUpdated": "2026-09-13T06:32:21.616Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-15T06:19:15+00:00",
      "cve": "CVE-2026-89641",
      "id": "CVE-2026-89641",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "185",
      "product_status:known_not_affected": "91",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89641.json",
      "version": "3"
    }
  }
}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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