CVE-2025-39942 (GCVE-0-2025-39942)

Vulnerability from cvelistv5 – Published: 2025-10-04 07:31 – Updated: 2026-08-05 12:06
VLAI
Title
ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size This is inspired by the check for data_offset + data_length.
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
Linux Linux Affected: 2ea086e35c3d726a3bacd0a971c1f02a50e98206 , < 196a3a7676d726ee67621ea2bf3b7815ac2685b4 (git)
Affected: 2ea086e35c3d726a3bacd0a971c1f02a50e98206 , < d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce (git)
Affected: 2ea086e35c3d726a3bacd0a971c1f02a50e98206 , < 9644798294c7287e65a7b26e35aa6d2ce3345bcc (git)
Affected: 2ea086e35c3d726a3bacd0a971c1f02a50e98206 , < c64b915bb3d9339adcae5db4be2c35ffbef5e615 (git)
Affected: 2ea086e35c3d726a3bacd0a971c1f02a50e98206 , < e1868ba37fd27c6a68e31565402b154beaa65df0 (git)
Create a notification for this product.
Linux Linux Affected: 5.15
Unaffected: 0 , < 5.15 (semver)
Unaffected: 6.1.154 , ≤ 6.1.* (semver)
Unaffected: 6.6.108 , ≤ 6.6.* (semver)
Unaffected: 6.12.49 , ≤ 6.12.* (semver)
Unaffected: 6.16.9 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
Create a notification for this product.
Show details on NVD website
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{
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              "value": "AV:N - The flaw is in ksmbd\u0027s in-kernel SMB Direct (RDMA) transport receive completion handler, which parses `smb_direct_data_transfer` headers straight off the wire from a remote SMB client on the SMB Direct port (5445/445 over iWARP or RoCEv2, both routable). No local access is needed \u2014 a single crafted RDMA send from a remote peer reaches the vulnerable code.\nAC:L - `remaining_data_length` is a plain header field the attacker writes directly, and the attacker also controls `preferred_send_size` in the SMB Direct negotiate request that determines `max_fragmented_recv_size`, so the unsatisfiable-reassembly condition is set up deterministically with two packets. No race, no memory-layout grooming, no timing dependency.\nPR:N - `recv_done()` is transport-level code that runs on every data transfer message before any SMB2 session setup or credential verification, and ksmbd never validates the negotiate request\u0027s `preferred_send_size`, letting an unauthenticated peer shrink the reassembly capacity below the pre-auth `SMB3_MAX_MSGSIZE` PDU limit and wedge the connection thread with no credentials at all.\nUI:N - The server processes the malformed data transfer message automatically as part of normal SMB Direct receive completion handling. No administrator or user action on the target is involved.\nS:U - The impact is confined to the ksmbd server\u0027s own kernel context \u2014 the stalled connection thread and pinned kernel allocations \u2014 with no crossing into a different security authority such as a hypervisor or IOMMU boundary.\nC:N - With the parent commit\u0027s `data_offset`/`data_length` validation in place, every `memcpy()` source in `smb_direct_read()` stays within the DMA\u0027d `wc-\u003ebyte_len` region, so no out-of-bounds or stale buffer contents are read and nothing is disclosed to the attacker beyond data they supplied themselves.\nI:N - The unsigned overflow of `data_length + remaining_data_length` only desynchronizes RFC1002 PDU framing on a byte stream the attacker already fully controls, and `get_rfc1002_len()`\u0027s `0xFFFFFF` mask plus the `max_allowed_pdu_size` check prevent any under-allocation or out-of-bounds write, so no kernel data or control flow is modified.\nA:H - A remote peer can request reassembly of a message larger than the transport can ever hold (bounded by 255 recvmsg buffers), permanently blocking the ksmbd connection kthread in `wait_event_interruptible()` while it pins a multi-megabyte `kvmalloc` buffer and the entire receive buffer pool; repeating this across connections exhausts kernel memory and server threads, denying SMB service."
            }
          ]
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      "providerMetadata": {
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        "shortName": "Linux"
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    "datePublished": "2025-10-04T07:31:04.810Z",
    "dateReserved": "2025-04-16T07:20:57.148Z",
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    "state": "PUBLISHED"
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    },
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      "cve": "CVE-2025-39942",
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      "title": "ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size",
      "url": "https://msrc.microsoft.com/csaf/vex/2025/msrc_cve-2025-39942.json",
      "version": "1"
    },
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-30T10:24:56+00:00",
      "cve": "CVE-2025-39942",
      "id": "CVE-2025-39942",
      "initial_release_date": "2025-10-04T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39942.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-07-31T01:05:07Z",
      "cve": "CVE-2025-39942",
      "id": "CVE-2025-39942",
      "initial_release_date": "2025-10-06T23:27:04Z",
      "product_status:known_not_affected": "416",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-39942",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-39942.json",
      "version": "7"
    }
  }
}



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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.