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Review reviewHigh

CVE-2026-63909

Linux

In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->si...

CVSS
8.1
EPSS
-
- percentile
CISA KEV
Not listed
Published
2026.07.20
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability-
Technical severityCVSS 8.1

Vulnerability overview

In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->si...

Affected product and versions

Product
Linux
Affected versions
>= 282cbbb476b9f35793452bc461934af4c7eca169 < 5500ba1d410aed1eded3eb04a76b10cfb4409334, >= f20adc4ef7428bc485ee83fd1a592252fb87718b < f6324b4240cf0b26a84c33f68a1222d727ff4af2, >= 325d4ac11f526cb8964cff14548ccf02d8c756d8 < 0fe08c5776a798f46df1fd74b331be26bdd644d6, >= 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c < d333af32e4451285e427f2d9c29de3a39f6f6d48, >= 90089584b2e25c4510b7b987387b4405f0673ece < 94215d55b09445993929f4fc966061d61de74929, >= 151b1799861fde38087c08f613abc2843ef597b0 < 4f7c131d2bdd7cd64b96f60d10be5ea72253f520, >= d07b26f39246a82399661936dd0c853983cfade7 < 0e60dafe97eca61721f3db456f97d97a80c6c8ae, >= 6.6.140 < 6.6.143, >= 6.12.84 < 6.12.93, >= 6.18.25 < 6.18.35, >= 7.0.2 < 7.0.12
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Linux and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
CWE
Not available
CVE-2026-63909 — Linux | SECUFOCUS NOW