Strix
26.1K

CVE-2026-63909

HIGHCVSS 8.1/10EPSS 0.63%

Last modified

CVE-2026-63909 is a high-severity vulnerability rated 8.1/10 on the CVSS scale. 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->size` (offset 2) even when `aces_size` is 0-3 bytes. EPSS estimates a 0.63% chance of exploitation in the next 30 days.

Description

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->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().

Metrics

CVSS 3.1
8.1/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

EPSS Probability
0.63%

46.4th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
LinuxLinux>= 282cbbb476b9f35793452bc461934af4c7eca169, < 5500ba1d410aed1eded3eb04a76b10cfb4409334; >= f20adc4ef7428bc485ee83fd1a592252fb87718b, < f6324b4240cf0b26a84c33f68a1222d727ff4af2; >= 325d4ac11f526cb8964cff14548ccf02d8c756d8, < 0fe08c5776a798f46df1fd74b331be26bdd644d6; >= 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c, < d333af32e4451285e427f2d9c29de3a39f6f6d48; >= 90089584b2e25c4510b7b987387b4405f0673ece, < 94215d55b09445993929f4fc966061d61de74929; >= 151b1799861fde38087c08f613abc2843ef597b0, < 4f7c131d2bdd7cd64b96f60d10be5ea72253f520; >= d07b26f39246a82399661936dd0c853983cfade7, < 0e60dafe97eca61721f3db456f97d97a80c6c8ae
LinuxLinux>= 6.6.140, < 6.6.143; >= 6.12.84, < 6.12.93; >= 6.18.25, < 6.18.35; >= 7.0.2, < 7.0.12

References

Timeline

Published
Last Modified
Status
Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-63909?
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->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().
How severe is CVE-2026-63909?
CVE-2026-63909 has a CVSS score of 8.1/10 (HIGH severity). The EPSS model estimates a 0.63% probability of exploitation in the next 30 days.
How do I fix CVE-2026-63909?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

Related CVEs from 2026

View all 2026CVEs →

Are you affected by CVE-2026-63909?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST