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CVE Record

CVE-2026-43379: ksmbd: fix use-after-free in smb_lazy_parent_lease_break_close()

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free in smb_lazy_parent_lease_break_close() opinfo pointer obtained via rcu_dereference(fp->f_opinfo) is being accessed after rcu_read_unlock() has been called. This creates a race condition where the memory could be freed by a concurrent writer between the unlock and the subsequent pointer dereferences (opinfo->is_lease, etc.), leading to a use-after-free.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A race condition in Linux's ksmbd SMB server can leave the kernel using memory after it has been freed. The supplied CVSS assessment indicates possible compromise of confidentiality, integrity, and availability without authentication or user interaction. Actual exploitability and observed impact are not established by the supplied evidence.

Executive priority

Treat internet-facing or untrusted-network ksmbd systems as urgent. Prioritize exposure identification, vendor-supported kernel updates, and temporary network restrictions. Systems where ksmbd is absent or disabled can receive lower priority after that status is verified.

Technical view

ksmbd obtains fp->f_opinfo through rcu_dereference(), but later reads fields such as is_lease after rcu_read_unlock(). A concurrent writer can free the referenced object during that interval, causing a use-after-free. Linux stable kernel commits are linked as fixes for affected branches.

Likely exposure

Exposure is most concerning where ksmbd is enabled and reachable from untrusted networks. Systems not using ksmbd are unlikely to exercise the vulnerable path. The supplied affected-version metadata mixes release numbers and commit identifiers, so confirm exposure against the distribution's kernel package and branch-specific backport records.

Exploitation context

The supplied CVSS 9.8 vector describes a network-accessible, low-complexity issue requiring neither privileges nor user interaction. However, the CVE is not listed as KEV, and the supplied sources provide no evidence of active exploitation, public exploit code, or confirmed remote code execution.

Researcher notes

Review the linked stable commits to identify branch-specific backports. The bundle does not provide a CWE, reproducer, attack-path details, or proof of practical exploitation. Its unusual version metadata should not be interpreted without distribution advisories or commit-level verification.

Mitigation direction

  • Check Linux distribution guidance for affected packages and supported remediation.
  • Deploy a vendor-supported kernel containing the applicable stable fix or backport.
  • Restrict SMB access to trusted networks while remediation is pending.
  • Disable ksmbd where it is unnecessary, subject to operational approval.
  • Reboot into the updated kernel when required by vendor guidance.

Validation and detection

  • Inventory hosts running kernels that include or backport ksmbd.
  • Confirm whether ksmbd is enabled and serving SMB connections.
  • Compare kernel package changelogs with the linked stable fix commits.
  • Verify the running kernel after remediation, not only the installed package.
  • Retest SMB availability and access controls after updating.
Prepared
Confidence
high
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

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CVE-2026-43379 mapping review

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2026-43379Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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
LinuxLinux27b40b7bfcd121fe13a150ffe11957630cf49246, 5fb282ba4fef8985a5acf2b32681f2ec07732561, 5fb282ba4fef8985a5acf2b32681f2ec07732561, 5fb282ba4fef8985a5acf2b32681f2ec07732561, 5fb282ba4fef8985a5acf2b32681f2ec07732561, 6.6.32unaffected
LinuxLinux6.9, 0, 6.6.130, 6.12.78, 6.18.19, 6.19.9, 7.0affected
Weakness

CWE details

No CWE listed

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