High

CVE-2026-63909 — ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops

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().

Published Jul 19, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.6% (30-day exploitation probability)+7
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.63%

ahead of 49% of scored CVEs · Oct 15, 2026

Affects

Linux

CVSS base

8.1

High · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	≥ 282cbbb476b9f35793452bc461934af4c7eca169 and < 5500ba1d410aed1eded3eb04a76b10cfb4409334≥ f20adc4ef7428bc485ee83fd1a592252fb87718b and < f6324b4240cf0b26a84c33f68a1222d727ff4af2≥ 325d4ac11f526cb8964cff14548ccf02d8c756d8 and < 0fe08c5776a798f46df1fd74b331be26bdd644d6≥ 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c and < d333af32e4451285e427f2d9c29de3a39f6f6d48≥ 90089584b2e25c4510b7b987387b4405f0673ece and < 94215d55b09445993929f4fc966061d61de74929≥ 151b1799861fde38087c08f613abc2843ef597b0 and < 4f7c131d2bdd7cd64b96f60d10be5ea72253f520≥ d07b26f39246a82399661936dd0c853983cfade7 and < 0e60dafe97eca61721f3db456f97d97a80c6c8ae≥ 6.6.140 and < 6.6.143 and 3 more ≥ 6.12.84 and < 6.12.93≥ 6.18.25 and < 6.18.35≥ 7.0.2 and < 7.0.12	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.1	CVSS 3.1	High	2.8	5.2	416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
8.1	CVSS 3.1	High	—	—	Linux via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · linux/linux
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 8.1
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Awaiting Analysis
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Jul 19, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

7 on the record

git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334
NIST National Vulnerability Database
git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48
NIST National Vulnerability Database
git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2
NIST National Vulnerability Database
git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6
NIST National Vulnerability Database
git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929
NIST National Vulnerability Database
git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520
NIST National Vulnerability Database
git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 15h
Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 15h
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-63909 is "ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.1 describes technical severity. EPSS 0.63% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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