CVE-2025-39943Network attack vector

Kernel memory disclosure and crash via unchecked offsets

Published Oct 4, 2025 · Updated Oct 4, 2025

Out-of-bounds read in Linux kernel ksmbd 5.15 through 6.17-rc6 allows remote attackers to disclose memory or crash the host via SMB Direct. The recv_done path trusts data_offset and data_length from smb_direct_data_transfer and copies from beyond the received buffer into an SMB2 request. The flaw is reachable before SMB authentication when an SMB Direct listener is exposed; crafted offsets can leak kernel memory or fault kernel context.

CVSS severity9.4
Critical
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Linux kernel ksmbd 5.15 through 6.17-rc6 allows remote attackers to disclose memory or crash the host via SMB Direct. The recv_done path trusts data_offset and data_length from smb_direct_data_transfer and copies from beyond the received buffer into an SMB2 request. The flaw is reachable before SMB authentication when an SMB Direct listener is exposed; crafted offsets can leak kernel memory or fault kernel context.

The record

CVE
CVE-2025-39943
Published
Oct 4, 2025
Updated
Oct 4, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-125, T1190
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 <5282491fc49d5614ac6ddcd012e5743eecb6a67c
  2. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <529b121b00a6ee3c88fb3c01b443b2b81f686d48
  3. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <773fddf976d282ef059c36c575ddb81567acd6bc
  4. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <8be498fcbd5b07272f560b45981d4b9e5a2ad885
  5. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <bdaab5c6538e250a9654127e688ecbbeb6f771d5
  6. Affected versionversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <eb0378dde086363046ed3d7db7f126fc3f76fd70
  7. Affected versionversion=5.15

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <5282491fc49d5614ac6ddcd012e5743eecb6a67c; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <529b121b00a6ee3c88fb3c01b443b2b81f686d48; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <773fddf976d282ef059c36c575ddb81567acd6bc; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <8be498fcbd5b07272f560b45981d4b9e5a2ad885; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <bdaab5c6538e250a9654127e688ecbbeb6f771d5; version=2ea086e35c3d726a3bacd0a971c1f02a50e98206 <eb0378dde086363046ed3d7db7f126fc3f76fd70; version=5.15

Published CVSS scores

9.4Linux kernel CVE teamCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H
7.1NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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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

CWE-125Out-of-bounds Read
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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