CVE-2026-98175 (GCVE-0-2026-98175)
Vulnerability from cvelistv5
Published
2026-10-06 08:44
Modified
2026-10-19 09:15
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: cancel reconnect work in clean_demultiplex_info() clean_demultiplex_info() cancels server->echo delayed work but not server->reconnect, which can cause a use-after-free when the demultiplex thread exits while a reconnect work is still queued: cifs_demultiplex_thread() cifs_readv_from_socket() cifs_reconnect() __cifs_reconnect() cifs_queue_server_reconn() mod_delayed_work(cifsiod_wq, &server->reconnect, 0) clean_demultiplex_info() cancel_delayed_work_sync(&server->echo) // echo canceled // reconnect NOT canceled kfree_sensitive(server) // server freed ...later, on cifsiod_wq: smb2_reconnect_server() server->srv_count // UAF read of freed server Fix this by canceling server->reconnect delayed work in clean_demultiplex_info() before the server is freed, the same way cifs_put_tcp_session() already does.
References
Impacted products
Vendor Product Version
Linux Linux Version: 53e0e11efe9289535b060a51d4cf37c25e0d0f2b
Version: 53e0e11efe9289535b060a51d4cf37c25e0d0f2b
Version: 53e0e11efe9289535b060a51d4cf37c25e0d0f2b
Version: 53e0e11efe9289535b060a51d4cf37c25e0d0f2b
Version: 53e0e11efe9289535b060a51d4cf37c25e0d0f2b
Version: e008a962311a875a828cbae54b43285858aaa6c8
Version: 123b228a09b90b50b0a9d6eb8294cf0c42efc029
Version: 0ba4c6eaaacbcc4b18f51bb3b1567c65a8fecca9
Version: d0d2a4c82942e2f51e4984beea1f7e5a994bd06c
Version: 15a12fbbf365a483b1c19f9caeb707b3bea77e10
Version: f0b715409cb9cf7e21e690f9b163047739761962
Version: ff04da387c10b6bf7b510392742c8cd46c130fd6
Version: 48f9526f4dcb4b132fe0dc2450835311e3b013a6
Version: 3.10.107   ≤
Version: 3.12.70   ≤
Version: 3.16.42   ≤
Version: 3.18.47   ≤
Version: 4.1.38   ≤
Version: 4.4.40   ≤
Version: 4.8.16   ≤
Version: 4.9.1   ≤
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: cancel reconnect work in clean_demultiplex_info()\n\nclean_demultiplex_info() cancels server-\u003eecho delayed work but not\nserver-\u003ereconnect, which can cause a use-after-free when the\ndemultiplex thread exits while a reconnect work is still queued:\n\n  cifs_demultiplex_thread()\n    cifs_readv_from_socket()\n      cifs_reconnect()\n        __cifs_reconnect()\n          cifs_queue_server_reconn()\n            mod_delayed_work(cifsiod_wq, \u0026server-\u003ereconnect, 0)\n    clean_demultiplex_info()\n      cancel_delayed_work_sync(\u0026server-\u003eecho)   // echo canceled\n                                                 // reconnect NOT canceled\n      kfree_sensitive(server)                    // server freed\n\n  ...later, on cifsiod_wq:\n\n  smb2_reconnect_server()\n    server-\u003esrv_count  // UAF read of freed server\n\nFix this by canceling server-\u003ereconnect delayed work in\nclean_demultiplex_info() before the server is freed, the same way\ncifs_put_tcp_session() already does."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The SMB server at the other end of the client\u0027s TCP connection triggers the bug. When it resets the connection or sends an oversized SMB response, cifs_demultiplex_thread() calls cifs_reconnect() and then __cifs_reconnect(), which queues server-\u003ereconnect via cifs_queue_server_reconn(). clean_demultiplex_info() then frees the server without cancelling that work.\nAC:H - The malicious server can force reconnects whenever it likes. The free, though, only happens when the client drops its last TCP session reference (umount or a session put, via cifs_put_tcp_session) inside the window where __cifs_reconnect has re-queued the reconnect work. Then smb2_reconnect_server must run after kfree(server). The server cannot produce that client-side timing on demand.\nPR:N - A remote SMB server needs no credentials on the client host to drop its own connection or send a malformed response that drives the client into __cifs_reconnect. Mounting locally is not a lower-privilege route: cifs_fs_type has no FS_USERNS_MOUNT, so a local attacker would need real CAP_SYS_ADMIN.\nUI:R - The client has to mount a share from the attacker\u0027s SMB server, and a demultiplex thread only exists after that mount. The free also needs the client to unmount or otherwise drop the session at the wrong moment.\nS:U - The freed struct TCP_Server_Info and the cifsiod_wq worker that uses it after free are both in the client kernel. No VM, IOMMU or sandbox boundary is crossed.\nC:H - smb2_reconnect_server() reads server-\u003esrv_count from the freed TCP_Server_Info. If a reallocated object puts a nonzero value there, the worker carries on and dereferences primary_server, the reconnect_mutex and the session lists, all of which a heap spray would control.\nI:H - With a nonzero srv_count in reclaimed memory, the worker increments it, takes reconnect_mutex, manipulates the ses and tcon lists and calls cifs_put_tcp_session on the stale pointer. Those are writes through attacker-shaped memory, so they can corrupt kernel data.\nA:H - syzbot reproduced this use-after-free of TCP_Server_Info in smb2_reconnect_server. A stale worker running on the shared cifsiod_wq workqueue can oops or panic the client kernel."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:15:06.742Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/180380272f116dbd2b0354c5c7872e112e519149"
        },
        {
          "url": "https://git.kernel.org/stable/c/e3f6a779433d13aafb5edab59e4f9313051e8a52"
        },
        {
          "url": "https://git.kernel.org/stable/c/7ab9ceedd860216fb97f2d8574cbe58b8906f42a"
        },
        {
          "url": "https://git.kernel.org/stable/c/2e5103e11a17c274715dd56cf185eeedccf686b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/c65eae6f61d1778ff7a82e4aae4080e26f486af1"
        }
      ],
      "title": "smb: client: cancel reconnect work in clean_demultiplex_info()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98175",
    "datePublished": "2026-10-06T08:44:19.155Z",
    "dateReserved": "2026-09-25T10:25:14.322Z",
    "dateUpdated": "2026-10-19T09:15:06.742Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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