CVE-2025-39942Network attack vector

SMB service denial via oversized fragment declaration

Published Oct 4, 2025 · Updated Oct 4, 2025

Denial of service in the Linux ksmbd SMB Direct transport allows remote attackers to interrupt SMB service via crafted RDMA packets. The recv_done handler failed to ensure that declared remaining and current data lengths fit within max_fragmented_recv_size before fragmented reassembly. An unauthenticated network peer with RDMA reachability can declare an impossible message size, blocking connection processing and pinning kernel memory until SMB availability is exhausted.

CVSS severity7.5
High
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux ksmbd SMB Direct transport allows remote attackers to interrupt SMB service via crafted RDMA packets. The recv_done handler failed to ensure that declared remaining and current data lengths fit within max_fragmented_recv_size before fragmented reassembly. An unauthenticated network peer with RDMA reachability can declare an impossible message size, blocking connection processing and pinning kernel memory until SMB availability is exhausted.

The record

CVE
CVE-2025-39942
Published
Oct 4, 2025
Updated
Oct 4, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 4, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <196a3a7676d726ee67621ea2bf3b7815ac2685b4
  2. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <9644798294c7287e65a7b26e35aa6d2ce3345bcc
  3. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <c64b915bb3d9339adcae5db4be2c35ffbef5e615
  4. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce
  5. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <e1868ba37fd27c6a68e31565402b154beaa65df0
  6. Affected versionversion=5.15

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <196a3a7676d726ee67621ea2bf3b7815ac2685b4; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <9644798294c7287e65a7b26e35aa6d2ce3345bcc; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <c64b915bb3d9339adcae5db4be2c35ffbef5e615; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <e1868ba37fd27c6a68e31565402b154beaa65df0; version=5.15

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.5kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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