CVE-2025-38527 (GCVE-0-2025-38527)
Vulnerability from cvelistv5
Published
2025-08-16 11:12
Modified
2026-08-05 12:02
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix use-after-free in cifs_oplock_break A race condition can occur in cifs_oplock_break() leading to a use-after-free of the cinode structure when unmounting: cifs_oplock_break() _cifsFileInfo_put(cfile) cifsFileInfo_put_final() cifs_sb_deactive() [last ref, start releasing sb] kill_sb() kill_anon_super() generic_shutdown_super() evict_inodes() dispose_list() evict() destroy_inode() call_rcu(&inode->i_rcu, i_callback) spin_lock(&cinode->open_file_lock) <- OK [later] i_callback() cifs_free_inode() kmem_cache_free(cinode) spin_unlock(&cinode->open_file_lock) <- UAF cifs_done_oplock_break(cinode) <- UAF The issue occurs when umount has already released its reference to the superblock. When _cifsFileInfo_put() calls cifs_sb_deactive(), this releases the last reference, triggering the immediate cleanup of all inodes under RCU. However, cifs_oplock_break() continues to access the cinode after this point, resulting in use-after-free. Fix this by holding an extra reference to the superblock during the entire oplock break operation. This ensures that the superblock and its inodes remain valid until the oplock break completes.
References
Impacted products
Vendor Product Version
Linux Linux Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: b98749cac4a695f084a5ff076f4510b23e353ecd
Version: 2429fcf06d3cb962693868ab0a927c9038f12a2d
Version: 1ee4f2d7cdcd4508cc3cbe3b2622d7177b89da12
Version: 53fc31a4853e30d6e8f142b824f724da27ff3e40
Version: 8092ecc306d81186a64cda42411121f4d35aaff4
Version: ebac4d0adf68f8962bd82fcf483936edd6ec095b
Version: 3.16.72   ≤
Version: 4.9.171   ≤
Version: 4.14.114   ≤
Version: 4.19.37   ≤
Version: 5.0.10   ≤
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix use-after-free in cifs_oplock_break\n\nA race condition can occur in cifs_oplock_break() leading to a\nuse-after-free of the cinode structure when unmounting:\n\n  cifs_oplock_break()\n    _cifsFileInfo_put(cfile)\n      cifsFileInfo_put_final()\n        cifs_sb_deactive()\n          [last ref, start releasing sb]\n            kill_sb()\n              kill_anon_super()\n                generic_shutdown_super()\n                  evict_inodes()\n                    dispose_list()\n                      evict()\n                        destroy_inode()\n                          call_rcu(\u0026inode-\u003ei_rcu, i_callback)\n    spin_lock(\u0026cinode-\u003eopen_file_lock)  \u003c- OK\n                            [later] i_callback()\n                              cifs_free_inode()\n                                kmem_cache_free(cinode)\n    spin_unlock(\u0026cinode-\u003eopen_file_lock)  \u003c- UAF\n    cifs_done_oplock_break(cinode)       \u003c- UAF\n\nThe issue occurs when umount has already released its reference to the\nsuperblock. When _cifsFileInfo_put() calls cifs_sb_deactive(), this\nreleases the last reference, triggering the immediate cleanup of all\ninodes under RCU. However, cifs_oplock_break() continues to access the\ncinode after this point, resulting in use-after-free.\n\nFix this by holding an extra reference to the superblock during the\nentire oplock break operation. This ensures that the superblock and\nits inodes remain valid until the oplock break completes."
        }
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        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
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            {
              "lang": "en",
              "value": "AV:N - The freeing side is driven entirely by a remote SMB peer \u2014 `smb2_is_valid_oplock_break()` (fs/smb/client/smb2misc.c:712) parses unsolicited SMB2 OPLOCK_BREAK/LEASE_BREAK PDUs off the socket and queues `cifs_oplock_break()`, and the server also controls the stalls (`filemap_fdatawrite`/`fdatawait`, tree disconnect) that widen the window. A malicious, compromised, or on-path SMB server (signing is frequently absent) reaches this over the network or WAN.\nAC:L - This is not a tight race: the attacker parks the worker indefinitely by refusing to complete writeback, so whenever the unmount lands the worker deterministically holds the last superblock reference, and it then releases the stall at a time of its choosing. The intervening `kill_sb` network round trips guarantee the RCU grace period elapses before `cifs_done_oplock_break(cinode)`, making the use-after-free reliable and infinitely repeatable.\nPR:N - The attacker is the remote SMB server or an on-path attacker and holds no credentials, account, or capability on the victim client; oplock/lease breaks are unsolicited server-to-client notifications handled by the demultiplex thread. Client-side mount configuration is a deployment condition, not an attacker privilege.\nUI:N - The CIFS mount is a standing deployment condition (fstab/autofs/systemd `.automount`/pam_mount), and the required unmount happens automatically on idle expiry, logout, or attacker-induced link loss \u2014 no person participates. Because the attacker can hold the oplock-break worker parked indefinitely, it need only wait for that automatic teardown rather than race any user action.\nS:U - The use-after-free corrupts kernel slab memory (`cifs_inode_cache`) within the same kernel security authority as the vulnerable CIFS client code. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - When the freed `openFileList` head is groomed to appear non-empty, `smb2_oplock_response()` reads `cinode-\u003elease_key` out of freed slab memory and transmits it to the attacker\u0027s server in the break acknowledgement \u2014 a repeatable kernel-heap infoleak \u2014 and dereferences `cinode-\u003enetfs.inode.i_sb-\u003es_fs_info` from the dead object. Controlling the reallocated object escalates this to arbitrary kernel memory disclosure.\nI:H - `spin_unlock(\u0026cinode-\u003eopen_file_lock)` and `cifs_done_oplock_break()`\u0027s `clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, \u0026cinode-\u003eflags)` are out-of-lifetime writes at fixed offsets into whatever object reclaims the freed `cifsInodeInfo`, and the attacker can refill that slab with inodes whose fields come from its own server responses. Combined with the wild `i_sb-\u003es_fs_info` dereference, this is the standard heap-grooming path to a write primitive and control-flow hijack.\nA:H - Operating on the freed `cifsInodeInfo` \u2014 spinlock manipulation, list traversal, and a bit clear on released slab memory \u2014 produces KASAN splats, slab corruption, and oops/panic, as reported in kernel.org bugzilla #220309. The remote server can retrigger the sequence at will on every mount cycle."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:02:40.247Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4256a483fe58af66a46cbf3dc48ff26e580d3308"
        },
        {
          "url": "https://git.kernel.org/stable/c/0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b"
        },
        {
          "url": "https://git.kernel.org/stable/c/2baaf5bbab2ac474c4f92c10fcb3310f824db995"
        },
        {
          "url": "https://git.kernel.org/stable/c/09bce2138a30ef10d8821c8c3f73a4ab7a5726bc"
        },
        {
          "url": "https://git.kernel.org/stable/c/da11bd4b697b393a207f19a2ed7d382a811a3ddc"
        },
        {
          "url": "https://git.kernel.org/stable/c/705c79101ccf9edea5a00d761491a03ced314210"
        }
      ],
      "title": "smb: client: fix use-after-free in cifs_oplock_break",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38527",
    "datePublished": "2025-08-16T11:12:20.843Z",
    "dateReserved": "2025-04-16T04:51:24.023Z",
    "dateUpdated": "2026-08-05T12:02:40.247Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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