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CVE Record

CVE-2026-31539: smb: smbdirect: introduce smbdirect_socket.recv_io.credits.available

In the Linux kernel, the following vulnerability has been resolved: smb: smbdirect: introduce smbdirect_socket.recv_io.credits.available The logic off managing recv credits by counting posted recv_io and granted credits is racy. That's because the peer might already consumed a credit, but between receiving the incoming recv at the hardware and processing the completion in the 'recv_done' functions we likely have a window where we grant credits, which don't really exist. So we better have a decicated counter for the available credits, which will be incremented when we posted new recv buffers and drained when we grant the credits to the peer.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A race condition in Linux SMB Direct receive-credit accounting can grant a remote peer credits that are not actually available. The documented impact is loss of availability, not data theft or alteration. Systems using affected kernels and exposing the relevant SMB Direct functionality deserve prompt review.

Executive priority

Treat as a high-priority availability issue for SMB Direct deployments, especially externally or broadly reachable systems. Accelerate inventory and vendor-confirmed patching. Lower the operational priority for systems where SMB Direct is absent or unreachable, while still confirming package status.

Technical view

The SMB Direct receive path counted posted receive buffers and granted credits without safely accounting for an in-flight completion window. A peer could consume a credit before recv_done processing, allowing nonexistent credits to be granted. The resolution introduces a dedicated available-credit counter, incremented for newly posted buffers and decremented when credits are granted.

Likely exposure

Exposure requires an affected Linux kernel using the SMB Direct path and network reachability from a peer. The bundle lists 6.18, 6.18.11, 6.19.1, and 7.0 as affected, but its version representation is incomplete or ambiguous. Confirm distribution-specific status.

Exploitation context

The CVSS assessment describes remote, low-complexity, unauthenticated exploitation requiring no user interaction, with availability impact only. However, the bundle provides no proof of exploitation, public exploit, or weaponization. The CVE is not listed as KEV.

Researcher notes

The vulnerability is a concurrency flaw in receive-credit bookkeeping, with the critical window between hardware receipt and recv_done completion processing. The dedicated available counter addresses over-granting. No CWE, crash mechanism, affected distribution matrix, public proof of concept, or active-exploitation evidence is supplied.

Mitigation direction

  • Identify systems running the listed or vendor-equivalent affected kernels.
  • Prioritize reachable systems that actively use SMB Direct.
  • Apply a distribution kernel update containing the applicable referenced stable fix.
  • If no validated update is available, consult the Linux distributor's security guidance.

Validation and detection

  • Record running kernel versions and distribution package revisions.
  • Determine whether SMB Direct is enabled and operational on each system.
  • Map distribution patches against the three referenced stable commit identifiers.
  • After updating, verify the running kernel includes the vendor-confirmed correction.
  • Regression-test SMB Direct workloads and monitor for availability failures.
Prepared
Confidence
medium
Sources
5

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-2026-31539 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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
4Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-31539Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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
LinuxLinux5fb9b459b3686e366640edd4e62805ef7b4de927, 5fb9b459b3686e366640edd4e62805ef7b4de927, 5fb9b459b3686e366640edd4e62805ef7b4de927unaffected
LinuxLinux6.18, 0, 6.18.11, 6.19.1, 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.