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CVE-2025-40285 (GCVE-0-2025-40285)

Vulnerability from cvelistv5 – Published: 2025-12-06 21:51 – Updated: 2026-08-05 12:09
VLAI
Title
smb/server: fix possible refcount leak in smb2_sess_setup()
Summary
In the Linux kernel, the following vulnerability has been resolved: smb/server: fix possible refcount leak in smb2_sess_setup() Reference count of ksmbd_session will leak when session need reconnect. Fix this by adding the missing ksmbd_user_session_put().
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 37a0e2b362b3150317fb6e2139de67b1e29ae5ff , < 6fc935f798d44a8eb8a5e6659198399fbf57b981 (git)
Affected: 450a844c045ff0895d41b05a1cbe8febd1acfcfd , < e671f9bb97805771380c98de944e2ceab6949188 (git)
Affected: a39e31e22a535d47b14656a7d6a893c7f6cf758c , < dcc51dfe6ff26b52cac106865a172ac982d78401 (git)
Affected: b95629435b84b9ecc0c765995204a4d8a913ed52 , < d37b2c81c83d6c0d5ca582f4fe73c672983f9e0d (git)
Affected: b95629435b84b9ecc0c765995204a4d8a913ed52 , < 379510a815cb2e64eb0a379cb62295d6ade65df0 (git)
Affected: 2107ab40629aeabbec369cf34b8cf0f288c3eb1b (git)
Affected: 6.1.121 , < 6.1.159 (semver)
Affected: 6.6.67 , < 6.6.117 (semver)
Affected: 6.12.6 , < 6.12.59 (semver)
Affected: 5.15.176 , < 5.16 (semver)
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Linux Linux Affected: 6.13
Unaffected: 0 , < 6.13 (semver)
Unaffected: 6.1.159 , ≤ 6.1.* (semver)
Unaffected: 6.6.117 , ≤ 6.6.* (semver)
Unaffected: 6.12.59 , ≤ 6.12.* (semver)
Unaffected: 6.17.9 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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          "product": "Linux",
          "programFiles": [
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              "versionType": "semver"
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              "lessThanOrEqual": "6.17.*",
              "status": "unaffected",
              "version": "6.17.9",
              "versionType": "semver"
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.18",
              "versionType": "original_commit_for_fix"
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.159",
                  "versionStartIncluding": "6.1.121",
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb/server: fix possible refcount leak in smb2_sess_setup()\n\nReference count of ksmbd_session will leak when session need reconnect.\nFix this by adding the missing ksmbd_user_session_put()."
        }
      ],
      "metrics": [
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd is the in-kernel SMB server on TCP/445, and the leak is driven entirely by remote SMB2 SESSION_SETUP and LOGOFF PDUs on the attacker\u0027s own TCP connections. No local access to the target is required.\nAC:L - The attacker controls both sides of the race \u2014 it pipelines the SESSION_SETUP requests that take the reference and issues the LOGOFF/PreviousSessionId request that flips conn-\u003estatus to NEED_RECONNECT \u2014 and the window is wide because ksmbd_conn_wait_idle()/ksmbd_conn_wait_idle_sess_id() hold that status for the duration of the teardown (up to 120 s). Failed attempts are harmless and can be retried indefinitely.\nPR:N - smb2_check_user_session() explicitly bypasses session validation for SMB2_SESSION_SETUP, and the session is registered in conn-\u003esessions before any credential check, so the leaking lookup is reached with zero credentials. On the common guest-mapped ksmbd share, ntlm_authenticate() skips password verification for user_guest(), so the LOGOFF that flips the connection to NEED_RECONNECT is also available unauthenticated.\nUI:N - The attacker opens its own connections and issues every request itself; no legitimate user or administrator action is involved.\nS:U - The leaked session object and its pinned file references are kernel resources within the same security authority as the ksmbd server; no VM, IOMMU, or sandbox boundary is crossed.\nC:N - Nothing is read out of bounds and nothing is transmitted back to the client on this error path \u2014 the only effect is that a reference count is never decremented, so no kernel data is disclosed.\nI:N - No memory is written out of bounds or freed early; the object simply outlives its intended lifetime, so no kernel data or control flow is modified.\nA:H - Each won race permanently leaks a struct ksmbd_session plus its entire file table, so open struct file/inode/dentry references are pinned forever (also blocking unmount), and the attack is replayable without limit over surviving connections, driving unbounded kernel memory and handle exhaustion to OOM and system hang."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:09:15.214Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/6fc935f798d44a8eb8a5e6659198399fbf57b981"
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        },
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        {
          "url": "https://git.kernel.org/stable/c/379510a815cb2e64eb0a379cb62295d6ade65df0"
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      "title": "smb/server: fix possible refcount leak in smb2_sess_setup()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40285",
    "datePublished": "2025-12-06T21:51:09.590Z",
    "dateReserved": "2025-04-16T07:20:57.184Z",
    "dateUpdated": "2026-08-05T12:09:15.214Z",
    "state": "PUBLISHED"
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      "date": "2026-09-16",
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-30T10:19:35+00:00",
      "cve": "CVE-2025-40285",
      "id": "CVE-2025-40285",
      "initial_release_date": "2025-12-06T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: smb/server: fix possible refcount leak in smb2_sess_setup()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40285.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-01T13:42:50Z",
      "cve": "CVE-2025-40285",
      "id": "CVE-2025-40285",
      "initial_release_date": "2025-12-08T00:22:58Z",
      "product_status:known_not_affected": "560",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-40285",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-40285.json",
      "version": "18"
    }
  }
}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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