CVE-2026-31478Network attack vector

SMB2 response miscalculation via hardcoded buffer offsets

Published Apr 22, 2026 · Updated Apr 22, 2026

Response-size miscalculation in Linux Kernel ksmbd allows remote attackers to trigger incorrect SMB2 buffer sizing via crafted requests. The smb2_query_dir, smb2_get_ea, get_file_stream_info, and smb2_ioctl paths pass hardcoded header lengths to smb2_calc_max_out_buf_len instead of each response structure's Buffer offset. The ksmbd server must be enabled and reachable; the upstream record does not disclose whether exploitation causes a crash, memory disclosure, or code execution.

CVSS severity9.8
Critical
EPSS probability0.50%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Response-size miscalculation in Linux Kernel ksmbd allows remote attackers to trigger incorrect SMB2 buffer sizing via crafted requests. The smb2_query_dir, smb2_get_ea, get_file_stream_info, and smb2_ioctl paths pass hardcoded header lengths to smb2_calc_max_out_buf_len instead of each response structure's Buffer offset. The ksmbd server must be enabled and reachable; the upstream record does not disclose whether exploitation causes a crash, memory disclosure, or code execution.

The record

CVE
CVE-2026-31478
Published
Apr 22, 2026
Updated
Apr 22, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 22, 2026Record 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=6.6
  2. Affected versionversion=9f297df20d93411c0b4ddad7f88ba04a7cd36e77 <9a7166f0ef8cbb7bb48dd05e2471d995566003f5
  3. Affected versionversion=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <0e55f63dd08f09651d39e1b709a91705a8a0ddcb
  4. Affected versionversion=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <4cb537ae4f37d7d0f617815ed4bed7173fb50861
  5. Affected versionversion=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <6aef1765d6807e0f027cd87f6ac973eb0879a46d
  6. Affected versionversion=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <80824c7e527b70cf9039534e60aff592e8f209d1
  7. Affected versionversion=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <c3a89e3ec1ccf64fa6a34e391e1581ebbcba8683
  8. Affected versionversion=f2283680a80571ca82d710bc6ecd8f8beac67d63 <70b4c414889492c522b6e4331562360f49be2361

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.6; version=9f297df20d93411c0b4ddad7f88ba04a7cd36e77 <9a7166f0ef8cbb7bb48dd05e2471d995566003f5; version=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <0e55f63dd08f09651d39e1b709a91705a8a0ddcb; version=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <4cb537ae4f37d7d0f617815ed4bed7173fb50861; version=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <6aef1765d6807e0f027cd87f6ac973eb0879a46d; version=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <80824c7e527b70cf9039534e60aff592e8f209d1; version=e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d <c3a89e3ec1ccf64fa6a34e391e1581ebbcba8683; version=f2283680a80571ca82d710bc6ecd8f8beac67d63 <70b4c414889492c522b6e4331562360f49be2361

Published CVSS scores

9.8kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1SUSECVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
3.1Amazon LinuxCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

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

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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