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CVE Record

CVE-2025-40084: ksmbd: transport_ipc: validate payload size before reading handle

In the Linux kernel, the following vulnerability has been resolved: ksmbd: transport_ipc: validate payload size before reading handle handle_response() dereferences the payload as a 4-byte handle without verifying that the declared payload size is at least 4 bytes. A malformed or truncated message from ksmbd.mountd can lead to a 4-byte read past the declared payload size. Validate the size before dereferencing. This is a minimal fix to guard the initial handle read.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux ksmbd component can read four bytes beyond a message’s declared boundary when ksmbd.mountd supplies malformed or truncated data. This may expose kernel memory or crash the system. The CVSS rating is 7.1, but exploitation requires local, low-privileged access; the supplied sources do not establish a remote attack path.

Executive priority

Prioritize patching ksmbd-enabled file servers and multi-user systems where untrusted local access exists. Internet exposure alone does not establish exploitability from the supplied evidence. Systems without active ksmbd are lower priority, but teams should verify that condition rather than assume it.

Technical view

handle_response() in ksmbd transport IPC treated the payload as a four-byte handle without first confirming sufficient payload length. The correction validates the size before dereferencing. The stated impacts are high confidentiality loss and high availability loss, with no integrity impact. The bundle does not document whether the out-of-bounds read is reliably controllable.

Likely exposure

Exposure is most likely on systems running affected Linux kernels with ksmbd and its userspace ksmbd.mountd service active. The supplied affected-version data includes 5.15, 6.1.158, 6.6.115, 6.12.56, 6.17.6, and 6.18, but its structure is ambiguous; confirm status through the system’s kernel distributor.

Exploitation context

The CVSS vector describes a local, low-complexity attack requiring low privileges and no user interaction. The bundle marks this CVE as absent from KEV and provides no evidence of active exploitation, a public exploit, or remote reachability. Successful abuse could potentially disclose data or disrupt availability.

Researcher notes

The supplied version metadata is not a clean range and includes unusual entries, so exact branch boundaries cannot be established confidently. Five stable-kernel commits are cited as fixes. Further assessment should compare distributor source packages against those changes and examine whether untrusted local actors can influence the ksmbd.mountd IPC response path.

Mitigation direction

  • Update to a vendor-supported kernel containing the applicable cited stable fix.
  • Check Linux distributor advisories for exact fixed package versions and backports.
  • Disable ksmbd where SMB file serving is unnecessary, subject to operational approval.
  • Restrict local access and privileges on systems that must continue running ksmbd.

Validation and detection

  • Inventory kernel versions and determine whether the ksmbd module is present or loaded.
  • Confirm whether ksmbd.mountd and SMB file-serving functionality are active.
  • Verify the installed kernel package includes the relevant upstream fix or distributor backport.
  • Review kernel logs for ksmbd faults or unexplained crashes, without treating absence as proof of safety.
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-2025-40084 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/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
7.1CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H1.85.2Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2025-40084Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/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
LinuxLinux0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cfunaffected
LinuxLinux5.15, 0, 6.1.158, 6.6.115, 6.12.56, 6.17.6, 6.18affected
Weakness

CWE details

No CWE listed

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