CVE-2026-64437 (GCVE-0-2026-64437)
Vulnerability from cvelistv5
Published
2026-07-25 08:51
Modified
2026-08-17 04:55
Severity ?
8.8 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL Commit f580d27e8928 ("ksmbd: fix use-after-free of a deferred file_lock on double SMB2_CANCEL") made smb2_cancel() skip a work whose state is KSMBD_WORK_CANCELLED, so its cancel_fn cannot be fired a second time. But KSMBD_WORK has three states (ACTIVE, CANCELLED, CLOSED), and the same freeing producer path is reached for CLOSED too: SMB2_CLOSE on the locking handle -> set_close_state_blocked_works() sets the deferred work's state to KSMBD_WORK_CLOSED and wakes the smb2_lock() worker. The worker takes the non-ACTIVE early-exit, locks_free_lock()s the file_lock and, because the state is not KSMBD_WORK_CANCELLED, takes the STATUS_RANGE_NOT_LOCKED branch with "goto out2" -- which, like the cancelled branch, skips release_async_work(). The work stays on conn->async_requests with a live cancel_fn = smb2_remove_blocked_lock pointing at the freed file_lock. A subsequent SMB2_CANCEL for the same AsyncId then passes the KSMBD_WORK_CANCELLED-only guard (its state is KSMBD_WORK_CLOSED), so smb2_cancel() fires cancel_fn again over the freed file_lock -- the same use-after-free fixed, via SMB2_CLOSE instead of a first SMB2_CANCEL: BUG: KASAN: slab-use-after-free in __locks_delete_block __locks_delete_block locks_delete_block ksmbd_vfs_posix_lock_unblock smb2_remove_blocked_lock smb2_cancel <- 2nd SMB2_CANCEL fires cancel_fn handle_ksmbd_work Allocated by ...: locks_alloc_lock <- smb2_lock Freed by ...: locks_free_lock <- smb2_lock (non-ACTIVE early-exit) ... cache file_lock_cache of size 192 Reproduced on mainline 7.1-rc7 (which already contains f580d27e8928) with KASAN by an authenticated SMB client; the double-SMB2_CANCEL control is silent on that kernel, so the splat is attributable to the CLOSE trigger. Only an ACTIVE deferred work may have its cancel_fn fired: both terminal states (CANCELLED and CLOSED) reach the smb2_lock() early-exit that frees the file_lock and skips release_async_work(). Guard on KSMBD_WORK_ACTIVE so any non-active work is skipped.
References
Impacted products
Vendor Product Version
Linux Linux Version: b7063c7426ea5a4d15e01b60538718765392f49d
Version: 0da2e073f9cbf4985a0fd9acb71bc5ff599f8afd
Version: 89ae9df09d2c1fb4a4eb495c113a7ce1dca34147
Version: 14d2eee0193ac3cd1bf3d014373449f0b8d35d6d
Version: f580d27e8928828693df44ba2db0fffdbe11dfea
Version: f580d27e8928828693df44ba2db0fffdbe11dfea
Version: 2b2eda2821cff1d1b5a423b6ee7d8fc6fbc8e694
Version: 6.1.176   ≤
Version: 6.6.143   ≤
Version: 6.12.94   ≤
Version: 6.18.36   ≤
Version: 7.0.13   ≤
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smb2pdu.c"
          ],
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              "status": "affected",
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          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smb2pdu.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "lessThan": "7.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
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              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.145",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.96",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.39",
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            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                  "vulnerable": true
                },
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                  "versionStartIncluding": "6.6.143",
                  "vulnerable": true
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                  "vulnerable": true
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                },
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL\n\nCommit f580d27e8928 (\"ksmbd: fix use-after-free of a deferred file_lock on\ndouble SMB2_CANCEL\") made smb2_cancel() skip a work whose state is\nKSMBD_WORK_CANCELLED, so its cancel_fn cannot be fired a second time. But\nKSMBD_WORK has three states (ACTIVE, CANCELLED, CLOSED), and the same\nfreeing producer path is reached for CLOSED too:\n\n  SMB2_CLOSE on the locking handle -\u003e set_close_state_blocked_works() sets\n  the deferred work\u0027s state to KSMBD_WORK_CLOSED and wakes the smb2_lock()\n  worker. The worker takes the non-ACTIVE early-exit, locks_free_lock()s\n  the file_lock and, because the state is not KSMBD_WORK_CANCELLED, takes\n  the STATUS_RANGE_NOT_LOCKED branch with \"goto out2\" -- which, like the\n  cancelled branch, skips release_async_work(). The work stays on\n  conn-\u003easync_requests with a live cancel_fn = smb2_remove_blocked_lock\n  pointing at the freed file_lock.\n\nA subsequent SMB2_CANCEL for the same AsyncId then passes the\nKSMBD_WORK_CANCELLED-only guard (its state is KSMBD_WORK_CLOSED), so\nsmb2_cancel() fires cancel_fn again over the freed file_lock -- the same\nuse-after-free fixed, via SMB2_CLOSE instead of a first SMB2_CANCEL:\n\n  BUG: KASAN: slab-use-after-free in __locks_delete_block\n    __locks_delete_block\n    locks_delete_block\n    ksmbd_vfs_posix_lock_unblock\n    smb2_remove_blocked_lock\n    smb2_cancel                 \u003c- 2nd SMB2_CANCEL fires cancel_fn\n    handle_ksmbd_work\n  Allocated by ...: locks_alloc_lock \u003c- smb2_lock\n  Freed by ...:     locks_free_lock  \u003c- smb2_lock (non-ACTIVE early-exit)\n  ... cache file_lock_cache of size 192\n\nReproduced on mainline 7.1-rc7 (which already contains f580d27e8928) with\nKASAN by an authenticated SMB client; the double-SMB2_CANCEL control is\nsilent on that kernel, so the splat is attributable to the CLOSE trigger.\n\nOnly an ACTIVE deferred work may have its cancel_fn fired: both terminal\nstates (CANCELLED and CLOSED) reach the smb2_lock() early-exit that frees\nthe file_lock and skips release_async_work(). Guard on KSMBD_WORK_ACTIVE\nso any non-active work is skipped."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd processes attacker-supplied SMB2 requests over TCP port 445, so the complete vulnerable path is remotely network-reachable.\nAC:L - The attacker controls the conflicting file handles, deferred LOCK, CLOSE, and CANCEL requests and can pipeline or repeat them to win the cleanup race without relying on victim-controlled conditions.\nPR:L - The sequence is post-authentication: LOCK and CLOSE require a valid SMB session, authorized tree connection, and usable file handle, but only ordinary share-user rights and no administrative capabilities.\nUI:N - No victim action is required because the authenticated SMB client can create the conflicting locks and send the complete triggering sequence.\nS:U - The corruption occurs within the host kernel serving SMB and does not inherently cross a separate virtualization, sandbox, or IOMMU security authority.\nC:H - The stale 192-byte file_lock is dereferenced through attacker-timed slab reuse, including linked-list and waitqueue pointers, making kernel-memory disclosure reasonably exploitable.\nI:H - Operations such as list unlinking and waitqueue handling on the reclaimed object can corrupt kernel pointers and potentially provide arbitrary writes or control-flow hijacking.\nA:H - The confirmed slab use-after-free can cause a kernel oops or panic, and the remote client can repeatedly trigger the sequence."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:55:38.646Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a796ba4e61d5e14e07b79a359faac69f8f9b22a3"
        },
        {
          "url": "https://git.kernel.org/stable/c/b8e274e69ab09222c7a552c7c0c1eef9ce627fc1"
        },
        {
          "url": "https://git.kernel.org/stable/c/ddb9239828336b36d8a3ef5943fdffb2f55b6508"
        },
        {
          "url": "https://git.kernel.org/stable/c/94083db751930b1540ddff2b54d4677549c57f81"
        },
        {
          "url": "https://git.kernel.org/stable/c/12c36c99655f325befe50c26842f7deca414c381"
        },
        {
          "url": "https://git.kernel.org/stable/c/10f293a07f9e10e988b0ae44e2e99c631f5a68e0"
        }
      ],
      "title": "ksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64437",
    "datePublished": "2026-07-25T08:51:11.072Z",
    "dateReserved": "2026-07-19T15:36:31.788Z",
    "dateUpdated": "2026-08-17T04:55:38.646Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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