CVE-2026-31392

Cross-user SMB access via Kerberos session reuse

Published Apr 3, 2026 · Updated Apr 3, 2026

Credential confusion in the Linux kernel SMB client allows local users to mount Kerberos shares through another username's reused session. The match_session() Kerberos branch compares credential UIDs but previously ignored the requested username, so a later mount reused a prior SMB session despite a different username= option. Exploitation requires local high-privilege mount access and an existing Kerberos SMB session; it can expose or modify shares under the reused identity.

CVSS severity8.1
High
EPSS probability0.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Credential confusion in the Linux kernel SMB client allows local users to mount Kerberos shares through another username's reused session. The match_session() Kerberos branch compares credential UIDs but previously ignored the requested username, so a later mount reused a prior SMB session despite a different username= option. Exploitation requires local high-privilege mount access and an existing Kerberos SMB session; it can expose or modify shares under the reused identity.

The record

CVE
CVE-2026-31392
Published
Apr 3, 2026
Updated
Apr 3, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1550
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 3, 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=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <12b4c5d98cd7ca46d5035a57bcd995df614c14e1
  2. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <6e9ff1eb7feedcf46ff2d0503759960ab58e7775
  3. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2
  4. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9ee803bfdba0cf739038dbdabdd4c02582c8f2b2
  5. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <d33cbf0bf8979d779900da9be2505d68d9d8da25
  6. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <fd4547830720647d4af02ee50f883c4b1cca06e4

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linux Kernelversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <12b4c5d98cd7ca46d5035a57bcd995df614c14e1; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <6e9ff1eb7feedcf46ff2d0503759960ab58e7775; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9ee803bfdba0cf739038dbdabdd4c02582c8f2b2; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <d33cbf0bf8979d779900da9be2505d68d9d8da25; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <fd4547830720647d4af02ee50f883c4b1cca06e4

Published CVSS scores

8.1kernel.orgCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L

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)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1550Use Alternate Authentication Material

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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