CVE-2026-63909
ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops
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().
INFO
Published Date :
July 19, 2026, 4:17 p.m.
Last Modified :
July 27, 2026, 5:44 p.m.
Remotely Exploit :
Yes !
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
Solution
- Update the Linux kernel to include the fix.
- Ensure minimum ACE size checks are correctly implemented.
- Verify bounds checking in access control list processing.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-63909.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-63909 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-63909
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-63909 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-63909 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 20, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 19, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '282cbbb476b9f35793452bc461934af4c7eca169', 'lessThan': '5500ba1d410aed1eded3eb04a76b10cfb4409334', 'versionType': 'git'}, {'status': 'affected', 'version': 'f20adc4ef7428bc485ee83fd1a592252fb87718b', 'lessThan': 'f6324b4240cf0b26a84c33f68a1222d727ff4af2', 'versionType': 'git'}, {'status': 'affected', 'version': '325d4ac11f526cb8964cff14548ccf02d8c756d8', 'lessThan': '0fe08c5776a798f46df1fd74b331be26bdd644d6', 'versionType': 'git'}, {'status': 'affected', 'version': '95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c', 'lessThan': 'd333af32e4451285e427f2d9c29de3a39f6f6d48', 'versionType': 'git'}, {'status': 'affected', 'version': '90089584b2e25c4510b7b987387b4405f0673ece', 'lessThan': '94215d55b09445993929f4fc966061d61de74929', 'versionType': 'git'}, {'status': 'affected', 'version': '151b1799861fde38087c08f613abc2843ef597b0', 'lessThan': '4f7c131d2bdd7cd64b96f60d10be5ea72253f520', 'versionType': 'git'}, {'status': 'affected', 'version': 'd07b26f39246a82399661936dd0c853983cfade7', 'lessThan': '0e60dafe97eca61721f3db456f97d97a80c6c8ae', 'versionType': 'git'}], 'programFiles': ['fs/smb/server/smbacl.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '6.6.140', 'lessThan': '6.6.143', 'versionType': 'semver'}, {'status': 'affected', 'version': '6.12.84', 'lessThan': '6.12.93', 'versionType': 'semver'}, {'status': 'affected', 'version': '6.18.25', 'lessThan': '6.18.35', 'versionType': 'semver'}, {'status': 'affected', 'version': '7.0.2', 'lessThan': '7.0.12', 'versionType': 'semver'}], 'programFiles': ['fs/smb/server/smbacl.c'], 'defaultStatus': 'unaffected'}] Added 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(). Added Reference https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae Added Reference https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6 Added Reference https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520 Added Reference https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334 Added Reference https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929 Added Reference https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48 Added Reference https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2