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CVE Record

CVE-2025-40103: smb: client: Fix refcount leak for cifs_sb_tlink

In the Linux kernel, the following vulnerability has been resolved: smb: client: Fix refcount leak for cifs_sb_tlink Fix three refcount inconsistency issues related to `cifs_sb_tlink`. Comments for `cifs_sb_tlink` state that `cifs_put_tlink()` needs to be called after successful calls to `cifs_sb_tlink()`. Three calls fail to update refcount accordingly, leading to possible resource leaks.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-40103 is a Linux kernel SMB client issue where some successful link lookups fail to release a reference. The stated impact is possible resource leakage, not confirmed code execution or data theft. Business urgency depends on whether Linux systems use CIFS/SMB client mounts and how quickly vendor kernels carry the upstream fix.

Executive priority

Treat as a targeted kernel maintenance item, not an emergency based on current evidence. Raise priority for business-critical Linux file-share clients or systems showing resource exhaustion symptoms. Track vendor patches because upstream fixes exist but distribution package status is not supplied.

Technical view

The Linux kernel SMB client had three `cifs_sb_tlink` reference-count inconsistencies. Callers that successfully obtained a tlink did not always call `cifs_put_tlink()`, causing refcount leaks. Upstream stable commits address the bug across kernel branches. No CVSS, CWE, or detailed exploit preconditions are provided in the source bundle.

Likely exposure

Exposure is most likely on Linux systems using the kernel CIFS/SMB client for mounted Windows or Samba shares. The bundle lists Linux as affected and points to upstream stable fixes, but does not identify distributions, configurations, or package-level affected ranges.

Exploitation context

The source bundle does not report active exploitation, public exploit availability, or CISA KEV listing. The described failure mode is resource leakage from incorrect reference counting in the SMB client, so operational degradation is the clearest documented concern.

Researcher notes

Evidence is limited to the CVE record and Linux stable commit references. The affected-version data is coarse and includes upstream kernel branch markers rather than distribution packages. Further analysis should review the linked patches, affected call paths, and distro backports without assuming exploitability beyond resource leakage.

Mitigation direction

  • Update to a vendor kernel that includes the referenced upstream stable fix.
  • Consult Linux distribution advisories for backported package versions.
  • Prioritize systems that actively use CIFS or SMB client mounts.
  • Remove unnecessary SMB client mounts where business operations allow.
  • Monitor affected systems for abnormal kernel memory or resource growth.

Validation and detection

  • Inventory Linux hosts with CIFS or SMB client mounts configured.
  • Map running kernel versions to vendor advisories or upstream fixed commits.
  • Check kernel changelogs for `smb: client: Fix refcount leak for cifs_sb_tlink`.
  • Confirm patched systems are running the updated kernel after reboot.
  • Review monitoring for recurring resource growth on SMB client workloads.
Prepared
Confidence
medium
Sources
8

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-2025-40103 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
0ADP providers
7Source links

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
LinuxLinux8ceb984379462f94bdebef3288d569c6e1f912ea, 8ceb984379462f94bdebef3288d569c6e1f912ea, 8ceb984379462f94bdebef3288d569c6e1f912ea, 8ceb984379462f94bdebef3288d569c6e1f912ea, 8ceb984379462f94bdebef3288d569c6e1f912ea, 8ceb984379462f94bdebef3288d569c6e1f912eaunaffected
LinuxLinux3.7, 0, 5.15.203, 6.1.158, 6.6.114, 6.12.55, 6.17.5, 6.18affected
Weakness

CWE details

No CWE listed

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