Vulnerability-Lookup

GHSA-F4F3-66V7-CMRJ

Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-13 09:32

Details

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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-89641"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-11T20:19:49Z",
    "severity": "HIGH"
  },
  "details": "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.",
  "id": "GHSA-f4f3-66v7-cmrj",
  "modified": "2026-09-13T09:32:26Z",
  "published": "2026-09-11T21:31:35Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89641"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4bea15d9c7683218f57b8c1f5f0aa75cab76af8d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4f18c9e7ee464aaae5cd9fccdb943b3fcb4655d4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b96db32fed8dfb2478d7c208f89bf383beed1535"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

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

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32

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

Linux mitre root

References

3 references

URL	Tags
https://git.kernel.org/stable/c/4f18c9e7ee464aaae…
https://git.kernel.org/stable/c/4bea15d9c7683218f…
https://git.kernel.org/stable/c/b96db32fed8dfb247…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < 4f18c9e7ee464aaae5cd9fccdb943b3fcb4655d4 (git) Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < 4bea15d9c7683218f57b8c1f5f0aa75cab76af8d (git) Affected: 110fee6b9bb58a5c50047fc2594d415f741b591e , < b96db32fed8dfb2478d7c208f89bf383beed1535 (git)
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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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/inode.c"
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          "versions": [
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              "versionType": "git"
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              "lessThan": "4bea15d9c7683218f57b8c1f5f0aa75cab76af8d",
              "status": "affected",
              "version": "110fee6b9bb58a5c50047fc2594d415f741b591e",
              "versionType": "git"
            },
            {
              "lessThan": "b96db32fed8dfb2478d7c208f89bf383beed1535",
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              "version": "110fee6b9bb58a5c50047fc2594d415f741b591e",
              "versionType": "git"
            }
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            "fs/smb/client/inode.c"
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.18"
            },
            {
              "lessThan": "6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
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        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "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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            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "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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        "dateUpdated": "2026-09-13T06:32:21.616Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          "url": "https://git.kernel.org/stable/c/4bea15d9c7683218f57b8c1f5f0aa75cab76af8d"
        },
        {
          "url": "https://git.kernel.org/stable/c/b96db32fed8dfb2478d7c208f89bf383beed1535"
        }
      ],
      "title": "cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size()",
      "x_generator": {
        "engine": "bippy-1.2.0"
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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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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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