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CVE-2025-21955 (GCVE-0-2025-21955)

Vulnerability from cvelistv5 – Published: 2025-04-01 15:46 – Updated: 2026-08-05 11:55
VLAI
Title
ksmbd: prevent connection release during oplock break notification
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: prevent connection release during oplock break notification ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.
Severity
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 0626e6641f6b467447c81dd7678a69c66f7746cf , < 09aeab68033161cb54f194da93e51a11aee6144b (git)
Affected: 0626e6641f6b467447c81dd7678a69c66f7746cf , < a4261bbc33fbf99b99c80aa3a2c5097611802980 (git)
Affected: 0626e6641f6b467447c81dd7678a69c66f7746cf , < f17d1c63a76b0fe8e9c78023a86507a3a6d62cfa (git)
Affected: 0626e6641f6b467447c81dd7678a69c66f7746cf , < 3aa660c059240e0c795217182cf7df32909dd917 (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.15
Unaffected: 0 , < 5.15 (semver)
Unaffected: 6.6.84 , ≤ 6.6.* (semver)
Unaffected: 6.12.20 , ≤ 6.12.* (semver)
Unaffected: 6.13.8 , ≤ 6.13.* (semver)
Unaffected: 6.14 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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{
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          "programFiles": [
            "fs/smb/server/connection.c",
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: prevent connection release during oplock break notification\n\nksmbd_work could be freed when after connection release.\nIncrement r_count of ksmbd_conn to indicate that requests\nare not finished yet and to not release the connection."
        }
      ],
      "metrics": [
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          "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"
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              "lang": "en",
              "value": "AV:N - ksmbd is the in-kernel SMB server listening on TCP/445; the entire path (oplock grant, oplock break trigger, and the connection reset that wins the race) is driven purely by SMB2 traffic from remote clients.\nAC:L - The attacker owns both sides of the race \u2014 connection A holds the oplock, connection B triggers the break notification, and the attacker chooses exactly when to reset A\u0027s socket \u2014 and can retry the sequence unlimited times over the network.\nPR:L - Reaching an oplock/lease break requires an established SMB2 session and tree connect (SMB2_CREATE with an oplock or lease context), so valid low-privileged share credentials (or a guest mapping) are needed; it is not a pre-authentication code path.\nUI:N - No victim action is required \u2014 the attacker\u0027s own two connections create the oplock, trigger the break, and tear down the connection entirely on their own schedule.\nS:U - The use-after-free is confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The freed ksmbd_conn/tcp_transport objects are dereferenced after release, and reclaiming those kmalloc-64 slots with attacker-sprayed data yields a read primitive over kernel memory and leaks server/session state.\nI:H - ksmbd_conn_write() performs an indirect call through conn-\u003etransport-\u003eops-\u003ewritev read out of the freed transport, giving control-flow hijack and arbitrary-write potential once the slab is reclaimed with controlled contents.\nA:H - Even without successful grooming the stale dereference of the freed connection, transport, and released socket reliably oopses or panics the kernel, killing the SMB server host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:55:35.788Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "cveId": "CVE-2025-21955",
    "datePublished": "2025-04-01T15:46:55.724Z",
    "dateReserved": "2024-12-29T08:45:45.790Z",
    "dateUpdated": "2026-08-05T11:55:35.788Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-09-16",
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Incremente r_count de ksmbd_conn para indicar que las solicitudes a\u00fan no han finalizado y para no liberar la 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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-30T10:19:08+00:00",
      "cve": "CVE-2025-21955",
      "id": "CVE-2025-21955",
      "initial_release_date": "2025-04-01T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: prevent connection release during oplock break notification",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-21955.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-02T01:19:37Z",
      "cve": "CVE-2025-21955",
      "id": "CVE-2025-21955",
      "initial_release_date": "2025-04-02T08:57:17Z",
      "product_status:known_not_affected": "568",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-21955",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-21955.json",
      "version": "10"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • 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.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • 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.


Detection rules are retrieved from Rulezet.


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