CVE-2025-40039 (GCVE-0-2025-40039)
Vulnerability from cvelistv5
Published
2025-10-28 11:48
Modified
2026-08-05 12:07
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 race condition in RPC handle list access The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd session. Access to this list is intended to be protected by 'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was flawed, leading to potential race conditions. In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock before calling xa_store() and xa_erase(). Since these operations modify the XArray structure, a write lock is required to ensure exclusive access and prevent data corruption from concurrent modifications. Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load() without holding any lock at all. This could lead to reading inconsistent data or a potential use-after-free if an entry is concurrently removed and the pointer is dereferenced. Fix these issues by: 1. Using down_write() and up_write() in ksmbd_session_rpc_open() to ensure exclusive access during XArray modification, and ensuring the lock is correctly released on error paths. 2. Adding down_read() and up_read() in ksmbd_session_rpc_method() to safely protect the lookup.
References
Impacted products
Vendor Product Version
Linux Linux Version: a4348710a7267705b75692dc1a000920481d1d92
Version: b685757c7b08d5073046fb379be965fd6c06aafc
Version: b685757c7b08d5073046fb379be965fd6c06aafc
Version: b685757c7b08d5073046fb379be965fd6c06aafc
Version: b685757c7b08d5073046fb379be965fd6c06aafc
Version: 1f485b54d04a920723984062c912174330a05178
Version: 052b41ef2abe274f068e892aee81406f11bd1f3a
Version: 5.15.145   ≤
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{
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          "defaultStatus": "unaffected",
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          "programFiles": [
            "fs/smb/server/mgmt/user_session.c"
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          "nodes": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: Fix race condition in RPC handle list access\n\nThe \u0027sess-\u003erpc_handle_list\u0027 XArray manages RPC handles within a ksmbd\nsession. Access to this list is intended to be protected by\n\u0027sess-\u003erpc_lock\u0027 (an rw_semaphore). However, the locking implementation was\nflawed, leading to potential race conditions.\n\nIn ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock\nbefore calling xa_store() and xa_erase(). Since these operations modify\nthe XArray structure, a write lock is required to ensure exclusive access\nand prevent data corruption from concurrent modifications.\n\nFurthermore, ksmbd_session_rpc_method() accessed the list using xa_load()\nwithout holding any lock at all. This could lead to reading inconsistent\ndata or a potential use-after-free if an entry is concurrently removed and\nthe pointer is dereferenced.\n\nFix these issues by:\n1. Using down_write() and up_write() in ksmbd_session_rpc_open()\n   to ensure exclusive access during XArray modification, and ensuring\n   the lock is correctly released on error paths.\n2. Adding down_read() and up_read() in ksmbd_session_rpc_method()\n   to safely protect the lookup."
        }
      ],
      "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 - The vulnerable code is in ksmbd, the in-kernel SMB server, and is driven entirely by SMB2 requests (CREATE/CLOSE/IOCTL/READ/WRITE/QUERY_INFO) arriving over TCP port 445 from a remote peer. No local access is needed.\nAC:L - The attacker controls both sides of the race: the pipe handle is an attacker-chosen VolatileFileId, and ksmbd_queue_work() executes each SMB2 request on a separate ksmbd-io worker (plus SMB3 multichannel), so concurrent SMB2_CLOSE and SMB2_IOCTL/READ/WRITE requests run in parallel with unlimited retries.\nPR:L - Reaching create_smb2_pipe() requires a session in SMB2_SESSION_VALID state (ksmbd_session_lookup_all() rejects IN_PROGRESS) plus a tree connect to IPC$, i.e. any valid low-privileged SMB account; no administrative rights are needed, and with guest mapping enabled even credentials are unnecessary.\nUI:N - The entire sequence is performed by the attacker\u0027s own SMB client against the server; no action by any local user or administrator is required.\nS:U - The use-after-free corrupts kernel heap state within the same kernel security authority; no hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - The unlocked xa_load() dereferences a kfree()\u0027d struct ksmbd_session_rpc, disclosing reused kernel heap contents as the RPC method flags; a UAF of this kind gives control over freed-object contents and can be leveraged into arbitrary kernel memory disclosure, and the resulting flags can steer the root ksmbd.mountd daemon into SAMR/LSARPC handlers the client never opened.\nI:H - The stale entry-\u003emethod value read from a reused 8-byte slab object is heap-groomable by the attacker and directly selects which privileged RPC method the root-privileged userspace daemon executes with client-supplied payload; use-after-free conditions are generally leverageable into arbitrary-write and control-flow hijack primitives.\nA:H - Dereferencing the freed entry after the slab object or page has been released oopses the ksmbd worker thread, and the unsynchronized RPC handle teardown corrupts session state, yielding a repeatable remote kernel crash / denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:07:13.052Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/69674b029002b1d90b655f014bdf64f404efa54d"
        },
        {
          "url": "https://git.kernel.org/stable/c/6b615a8fb3af0baf8126cde3d4fee97d57222ffc"
        },
        {
          "url": "https://git.kernel.org/stable/c/5cc679ba0f4505936124cd4179ba66bb0a4bd9f3"
        },
        {
          "url": "https://git.kernel.org/stable/c/6bd7e0e55dcea2cf0d391bbc21c2eb069b4be3e1"
        },
        {
          "url": "https://git.kernel.org/stable/c/305853cce379407090a73b38c5de5ba748893aee"
        }
      ],
      "title": "ksmbd: Fix race condition in RPC handle list access",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40039",
    "datePublished": "2025-10-28T11:48:19.781Z",
    "dateReserved": "2025-04-16T07:20:57.153Z",
    "dateUpdated": "2026-08-05T12:07:13.052Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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