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CVE Record

CVE-2026-43376: ksmbd: fix use-after-free by using call_rcu() for oplock_info

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free by using call_rcu() for oplock_info ksmbd currently frees oplock_info immediately using kfree(), even though it is accessed under RCU read-side critical sections in places like opinfo_get() and proc_show_files(). Since there is no RCU grace period delay between nullifying the pointer and freeing the memory, a reader can still access oplock_info structure after it has been freed. This can leads to a use-after-free especially in opinfo_get() where atomic_inc_not_zero() is called on already freed memory. Fix this by switching to deferred freeing using call_rcu().

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A memory-management flaw in Linux ksmbd can allow oplock data to be accessed after it is freed. The supplied CVSS rates it 9.8 and remotely reachable without authentication, indicating potentially severe compromise or disruption where ksmbd is exposed. The sources do not establish real-world exploitation.

Executive priority

Treat this as urgent for systems actively serving SMB through ksmbd, especially network-accessible hosts. Rapidly inventory affected systems and schedule vendor-supported kernel updates. Systems not using ksmbd have lower practical exposure, but their package status should still be verified.

Technical view

ksmbd immediately frees oplock_info with kfree() while opinfo_get() and proc_show_files() may retain RCU-protected references. Without an RCU grace period, atomic_inc_not_zero() can access freed memory. The referenced fix defers reclamation through call_rcu(). The sources do not document a complete attack path.

Likely exposure

Exposure is most likely on Linux systems using ksmbd to provide network-accessible SMB services. The bundle lists multiple upstream releases and revisions, but its flattened version information is insufficient for reliable distribution-package mapping. Confirm exposure through vendor advisories and backport records.

Exploitation context

The supplied record is not listed in KEV and contains no evidence of active exploitation, public weaponization, or observed attacks. CVSS 9.8 describes assessed technical potential, not confirmed exploitation. Trigger conditions beyond the underlying concurrent RCU access are not documented.

Researcher notes

Analysis should focus on oplock_info lifetime and races between pointer removal, RCU readers, and immediate freeing. The source explicitly identifies opinfo_get() and proc_show_files() as readers. Do not infer reliable code execution from the CVSS score alone; reproducibility and exploitation evidence are absent.

Mitigation direction

  • Prioritize vendor kernel updates incorporating the referenced call_rcu() fix.
  • Map distribution kernel packages and backports against the referenced stable commits.
  • If updating is delayed, follow distributor guidance; the supplied sources identify no separate mitigation.

Validation and detection

  • Confirm whether ksmbd is enabled and serving SMB on each Linux host.
  • Record running kernel and distribution package versions.
  • Verify the kernel contains the applicable stable fix or an acknowledged distributor backport.
  • After updating, confirm each host booted the remediated kernel.
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.

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CVE-2026-43376 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-2026-43376Attack 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
LinuxLinux296cb5457cc6f4a754c4ae29855f8a253d52bcc6, d54ab1520d43e95f9b2e22d7a05fc9614192e5a5, 18b4fac5ef17f77fed9417d22210ceafd6525fc7, 18b4fac5ef17f77fed9417d22210ceafd6525fc7, 18b4fac5ef17f77fed9417d22210ceafd6525fc7, d73686367ad68534257cd88a36ca3c52cb8b81d8, 6.6.88, 6.12.25, 6.14.4unaffected
LinuxLinux6.15, 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.