CVE-2026-64136 (GCVE-0-2026-64136)
Vulnerability from cvelistv5
Published
2026-07-19 15:40
Modified
2026-08-05 12:39
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: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked() Commit 96c4af418586 ("cifs: Fix locking usage for tcon fields") refactored cifs code to change cifs_tcp_ses_lock for tc_lock around tc_count changes. There was missing lock around tc_count increment inside smb2_find_smb_sess_tcon_unlocked().
References
Impacted products
Vendor Product Version
Linux Linux Version: 953953abb66e52c224057ab91e404284fefeab62
Version: 601dd3b79769b38d30b693c40afdb2a4b7edf9d0
Version: 3969db6b22e3d90d8c5f22ac1a7fe0350a94c136
Version: 96c4af418586ee9a6aab61738644366426e05316
Version: 96c4af418586ee9a6aab61738644366426e05316
Version: 8c59eeeeffa1524ef57e173a89a1a3ff539888d5
Version: 6.6.128   ≤
Version: 6.12.75   ≤
Version: 6.18.16   ≤
Version: 6.19.6   ≤
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()\n\nCommit 96c4af418586 (\"cifs: Fix locking usage for tcon fields\")\nrefactored cifs code to change cifs_tcp_ses_lock for tc_lock around\ntc_count changes.\n\nThere was missing lock around tc_count increment inside\nsmb2_find_smb_sess_tcon_unlocked()."
        }
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            "baseSeverity": "CRITICAL",
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            "version": "3.1"
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              "lang": "en",
              "value": "AV:N - The flaw is in the in-kernel SMB/CIFS client (fs/smb/client/), reached when processing SMB2 responses received over TCP from a remote server in cifs_demultiplex_thread(). A network-positioned attacker controlling or impersonating the SMB server can drive the vulnerable cancelled-mid handling path.\nAC:L - The attacker controls SMB response timing and can trigger concurrent cifs_put_tcon() via server-initiated disconnect/reconnect, racing the unprotected tc_count increment. Cancelled-mid conditions arise from normal concurrent I/O, signals, and unmount/reconnect activity that the attacker can reliably provoke.\nPR:N - Exploitation requires no local privileges on the victim; a remote malicious or compromised SMB server can attack any client that has an active CIFS mount/session, without the attacker holding an account or capabilities on the victim host.\nUI:N - No victim interaction is needed at exploit time in common deployments where CIFS shares are automounted at boot or persistently connected (cloud file shares, enterprise NAS); the attacker abuses an already-established SMB session rather than requiring a new mount action.\nS:U - Impact is kernel memory corruption and potential local privilege escalation within the same kernel security domain, not a cross-boundary escape such as guest-to-host VM breakout.\nC:H - The race can cause a use-after-free of struct cifs_tcon; UAF of kernel heap objects enables arbitrary memory disclosure through controlled reuse of the freed structure.\nI:H - The UAF leads to subsequent kernel operations (SMB2_close, workqueue handlers) on freed memory, providing a path to arbitrary kernel write and potential code execution via heap grooming.\nA:H - Winning the refcount race causes use-after-free of cifs_tcon with continued kernel use of the freed object, which can trigger kernel oops/panic and denial of service even before full exploitation."
            }
          ]
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      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:39:37.286Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d"
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          "url": "https://git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7"
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        {
          "url": "https://git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41"
        }
      ],
      "title": "smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64136",
    "datePublished": "2026-07-19T15:40:30.351Z",
    "dateReserved": "2026-07-19T07:54:57.036Z",
    "dateUpdated": "2026-08-05T12:39:37.286Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2"
}


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