LiveActive security incident?Get immediate response
CVE Record

CVE-2026-43490: ksmbd: validate inherited ACE SID length

In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate inherited ACE SID length smb_inherit_dacl() walks the parent directory DACL loaded from the security descriptor xattr. It verifies that each ACE contains the fixed SID header before using it, but does not verify that the variable-length SID described by sid.num_subauth is fully contained in the ACE. A malformed inheritable ACE can advertise more subauthorities than are present in the ACE. compare_sids() may then read past the ACE. smb_set_ace() also clamps the copied destination SID, but used the unchecked source SID count to compute the inherited ACE size. That could advance the temporary inherited ACE buffer pointer and nt_size accounting past the allocated buffer. Fix this by validating the parent ACE SID count and SID length before using the SID during inheritance. Compute the inherited ACE size from the copied SID so the size matches the bounded destination SID. Reject the inherited DACL if size accumulation would overflow smb_acl.size or the security descriptor allocation size.

HighCVSS 8.8Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A logged-in network user may be able to abuse a malformed inherited access-control entry on a Linux ksmbd file server. The kernel can read or calculate beyond allocated memory while applying inherited permissions, potentially causing disclosure, corruption, or service disruption. Systems not running ksmbd are unlikely to be exposed through this path.

Executive priority

Treat as a high-priority patching issue for exposed ksmbd servers, especially where less-trusted users can modify shared directories or permissions. Prioritize identification and containment promptly, but do not characterize this as an actively exploited emergency based on the supplied evidence.

Technical view

ksmbd's smb_inherit_dacl() validated the fixed SID header but not whether sid.num_subauth fit inside the ACE. A malformed inheritable ACE could trigger an out-of-bounds read in compare_sids() and incorrect inherited-buffer pointer and size accounting in smb_set_ace(). The fix validates SID length, derives size from the bounded copied SID, and rejects overflowing DACL sizes.

Likely exposure

Exposure requires Linux systems using ksmbd and processing inherited DACLs containing malformed ACE SID data. The CVSS vector indicates network reachability, low complexity, low privileges, and no user interaction. The supplied affected-version representation is ambiguous; confirm exposure against distribution advisories and the linked stable fixes.

Exploitation context

The supplied record is not in CISA KEV and provides no evidence of active exploitation or a public exploit. It describes a remotely reachable, authenticated condition involving malformed inheritable access-control data. Practical exploitability and the exact achievable impact are not established by the supplied sources.

Researcher notes

The vulnerability combines insufficient validation of a variable-length SID with unsafe size accumulation during DACL inheritance. The record supports possible out-of-bounds reading and advancement beyond a temporary allocation, but does not establish a specific corruption primitive, reliable code execution, affected configuration prevalence, or observed attacks.

Mitigation direction

  • Upgrade to a vendor-supported kernel containing the applicable linked stable fix.
  • Prioritize internet-accessible or untrusted-network systems running ksmbd.
  • Restrict SMB access to trusted networks and necessary authenticated users until patched.
  • Disable ksmbd where it is not operationally required.
  • Consult the Linux distribution vendor for exact fixed package versions.

Validation and detection

  • Confirm whether ksmbd is enabled or loaded on each Linux system.
  • Inventory kernel and distribution package versions on ksmbd hosts.
  • Compare installed kernels with vendor advisories and linked stable commits.
  • Review SMB exposure, authentication boundaries, and users able to modify inherited permissions.
  • After upgrading, verify the running kernel includes the applicable fix.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2026-43490 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
8.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
6Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.8CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H2.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

8.8High
CVSS 3.1 vector shape for CVE-2026-43490Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9unaffected
LinuxLinux5.15, 0, 6.6.141, 6.12.88, 6.18.30, 7.0.7, 7.1affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.