CVE-2026-39884Public exploitNetwork attack vector

Service exposure via space-split kubectl arguments

Published Apr 14, 2026 · Updated Apr 14, 2026

Argument injection in MCP Server Kubernetes 3.4.0 and earlier allows remote authenticated users to expose internal services via port_forward. The startPortForward function concatenates namespace, resource, and port fields into one kubectl string, then split(" ") turns embedded spaces into new flags. Access to the MCP tool is required; injected flags can bind a forward to all interfaces or override the intended Kubernetes namespace.

CVSS severity8.3
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Argument injection in MCP Server Kubernetes 3.4.0 and earlier allows remote authenticated users to expose internal services via port_forward. The startPortForward function concatenates namespace, resource, and port fields into one kubectl string, then split(" ") turns embedded spaces into new flags. Access to the MCP tool is required; injected flags can bind a forward to all interfaces or override the intended Kubernetes namespace.

The record

CVE
CVE-2026-39884
Published
Apr 14, 2026
Updated
Apr 14, 2026
Vendor
Flux159
Product
MCP Server Kubernetes
Classifications
CWE-88
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.5.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Flux159 · MCP Server Kubernetesversion=< 3.5.0

Published CVSS scores

8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
8.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-88Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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