CVE-2026-64401

Local kernel compromise via stale CIFS tcon

Published Jul 25, 2026 · Updated Jul 25, 2026

Use-after-free in the Linux kernel SMB client allows local users to execute code in kernel context through stale witness state. cifs_swn_notify() drops cifs_swnreg_idr_mutex and then dereferences a cached tcon pointer that can reference the freed first mount rather than a live same-share connection. A witness-enabled second mount must preserve the registration after the first tcon is freed; an unprivileged user can then trigger the stale dereference through world-readable /proc/fs/cifs/DebugData without mount authority.

CVSS severity7.0
High
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the Linux kernel SMB client allows local users to execute code in kernel context through stale witness state. cifs_swn_notify() drops cifs_swnreg_idr_mutex and then dereferences a cached tcon pointer that can reference the freed first mount rather than a live same-share connection. A witness-enabled second mount must preserve the registration after the first tcon is freed; an unprivileged user can then trigger the stale dereference through world-readable /proc/fs/cifs/DebugData without mount authority.

The record

CVE
CVE-2026-64401
Published
Jul 25, 2026
Updated
Jul 25, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 25, 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=5.11
  2. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <0700f946659d0ab2352ec8a9b1c6fc74b13a27d7
  3. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <51d18db392e5386a7bb9e816d611f14e600cca3c
  4. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <91b8a58c6ac15c7db6518f696389933282f88da7
  5. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <945b4a4a54497db1dcb2f20ef801a84e884dac21
  6. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd
  7. Affected versionversion=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <ec457f9afe5ae9538bdcd58fd4cb442b9787e183

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=5.11; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <0700f946659d0ab2352ec8a9b1c6fc74b13a27d7; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <51d18db392e5386a7bb9e816d611f14e600cca3c; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <91b8a58c6ac15c7db6518f696389933282f88da7; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <945b4a4a54497db1dcb2f20ef801a84e884dac21; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd; version=fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 <ec457f9afe5ae9538bdcd58fd4cb442b9787e183

Published CVSS scores

7.0Amazon LinuxCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

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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