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CVE Record

CVE-2026-31476: ksmbd: do not expire session on binding failure

In the Linux kernel, the following vulnerability has been resolved: ksmbd: do not expire session on binding failure When a multichannel session binding request fails (e.g. wrong password), the error path unconditionally sets sess->state = SMB2_SESSION_EXPIRED. However, during binding, sess points to the target session looked up via ksmbd_session_lookup_slowpath() -- which belongs to another connection's user. This allows a remote attacker to invalidate any active session by simply sending a binding request with a wrong password (DoS). Fix this by skipping session expiration when the failed request was a binding attempt, since the session does not belong to the current connection. The reference taken by ksmbd_session_lookup_slowpath() is still correctly released via ksmbd_user_session_put().

HighCVSS 8.2Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A remote, unauthenticated attacker can disrupt file-sharing users on Linux systems using ksmbd. A failed SMB multichannel binding request can wrongly expire another connection’s active session, interrupting access without needing valid credentials. The disclosed impact is primarily denial of service.

Executive priority

Prioritize remediation for internet-facing or broadly reachable ksmbd servers because disruption is unauthenticated and low complexity. Treat internal-only deployments as urgent where SMB availability supports business-critical workflows. Confirm exposure promptly, then patch through the operating-system vendor’s supported kernel channel.

Technical view

During SMB multichannel binding, ksmbd looks up the target session belonging to another connection. If authentication fails, the vulnerable error path marks that session expired. The kernel fix prevents session expiration for failed binding attempts while still releasing the acquired session reference. CVSS 3.1 is 8.2: network-accessible, low complexity, unauthenticated, with high availability impact.

Likely exposure

Exposure requires an affected Linux kernel with ksmbd enabled and reachable over the network. Systems not using ksmbd are unlikely to be exposed through this flaw. The supplied version data is ambiguous, so administrators should compare their exact distribution kernel against vendor guidance and the cited stable-kernel fixes.

Exploitation context

The described attack is remote, requires no privileges or user interaction, and uses an invalid-password multichannel binding request to terminate an active session. The supplied record is not in KEV and provides no evidence of active exploitation. No exploit code or confirmed exploitation campaign is cited.

Researcher notes

The flaw is a session-state ownership error in the binding failure path: the referenced session belongs to another connection, yet it is marked expired. The fix conditionally skips expiration for binding attempts and preserves reference release. The record’s affected-version list contains unusual and duplicated entries; use fix-commit presence or distribution advisories for reliable assessment.

Mitigation direction

  • Update to a vendor-supported kernel release containing the applicable cited ksmbd fix.
  • If immediate updating is impossible, restrict SMB access to trusted networks and authorized clients.
  • Disable ksmbd where kernel-hosted SMB service is unnecessary.
  • Review distribution advisories because backported fixes may not match upstream version numbers.

Validation and detection

  • Confirm whether ksmbd is enabled, loaded, and listening on network interfaces.
  • Record the running kernel build and compare it with distribution security guidance.
  • Verify the installed kernel contains the applicable cited stable-kernel fix.
  • Review logs for repeated binding failures followed by unexpected SMB session expirations.
  • After updating, confirm normal SMB sessions remain stable during authorized negative authentication testing.
Prepared
Confidence
high
Sources
9

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

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description · low confidence lookup

Credential and access behavior lookup

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cve · low confidence lookup

CVE-2026-31476 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.2 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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
8Source 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
8.2CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H3.94.2Linux

Vulnerability scoring details

Base CVSS 3.1 score

8.2High
CVSS 3.1 vector shape for CVE-2026-31476Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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
LinuxLinuxf5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1eff, f5a544e3bab78142207e0242d22442db85ba1effunaffected
LinuxLinux5.15, 0, 5.15.209, 6.1.168, 6.6.131, 6.12.80, 6.18.21, 6.19.11, 7.0affected
Weakness

CWE details

No CWE listed

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