CVE-2026-63909Network attack vector

Kernel memory disclosure via transposed ACE bounds check

Published Jul 19, 2026 · Updated Jul 19, 2026

Heap out-of-bounds read in Linux Kernel ksmbd allows remote authenticated users to read adjacent kernel memory or crash the host via SMB2. In smb_check_perm_dacl(), a transposed minimum-length comparison is always false, so the ACE walk reads ace->size two bytes beyond a short pntsd heap allocation. Reachability requires an authenticated SMB2 session with file creation and WRITE_DAC access on a ksmbd share that supports ACL extended attributes.

CVSS severity8.1
High
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap out-of-bounds read in Linux Kernel ksmbd allows remote authenticated users to read adjacent kernel memory or crash the host via SMB2. In smb_check_perm_dacl(), a transposed minimum-length comparison is always false, so the ACE walk reads ace->size two bytes beyond a short pntsd heap allocation. Reachability requires an authenticated SMB2 session with file creation and WRITE_DAC access on a ksmbd share that supports ACL extended attributes.

The record

CVE
CVE-2026-63909
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 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=151b1799861fde38087c08f613abc2843ef597b0 <4f7c131d2bdd7cd64b96f60d10be5ea72253f520
  2. Affected versionversion=282cbbb476b9f35793452bc461934af4c7eca169 <5500ba1d410aed1eded3eb04a76b10cfb4409334
  3. Affected versionversion=325d4ac11f526cb8964cff14548ccf02d8c756d8 <0fe08c5776a798f46df1fd74b331be26bdd644d6
  4. Affected versionversion=6.12.84 <6.12.93
  5. Affected versionversion=6.18.25 <6.18.35
  6. Affected versionversion=6.6.140 <6.6.143
  7. Affected versionversion=7.0.2 <7.0.12
  8. Affected versionversion=90089584b2e25c4510b7b987387b4405f0673ece <94215d55b09445993929f4fc966061d61de74929
  9. Affected versionversion=95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c <d333af32e4451285e427f2d9c29de3a39f6f6d48
  10. Affected versionversion=d07b26f39246a82399661936dd0c853983cfade7 <0e60dafe97eca61721f3db456f97d97a80c6c8ae
  11. Affected versionversion=f20adc4ef7428bc485ee83fd1a592252fb87718b <f6324b4240cf0b26a84c33f68a1222d727ff4af2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=151b1799861fde38087c08f613abc2843ef597b0 <4f7c131d2bdd7cd64b96f60d10be5ea72253f520; version=282cbbb476b9f35793452bc461934af4c7eca169 <5500ba1d410aed1eded3eb04a76b10cfb4409334; version=325d4ac11f526cb8964cff14548ccf02d8c756d8 <0fe08c5776a798f46df1fd74b331be26bdd644d6; version=6.12.84 <6.12.93; version=6.18.25 <6.18.35; version=6.6.140 <6.6.143; version=7.0.2 <7.0.12; version=90089584b2e25c4510b7b987387b4405f0673ece <94215d55b09445993929f4fc966061d61de74929; version=95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c <d333af32e4451285e427f2d9c29de3a39f6f6d48; version=d07b26f39246a82399661936dd0c853983cfade7 <0e60dafe97eca61721f3db456f97d97a80c6c8ae; version=f20adc4ef7428bc485ee83fd1a592252fb87718b <f6324b4240cf0b26a84c33f68a1222d727ff4af2

Published CVSS scores

8.1kernel.orgCVSS:3.1/AV:N/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

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

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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