Flux159 mcp-server-kubernetes up to 3.4.x Model Context Protocol port_forward.ts spawn argument injection

Summaryinfo

A vulnerability, which was classified as critical, has been found in Flux159 mcp-server-kubernetes up to 3.4.x. Impacted is the function spawn of the file src/tools/port_forward.ts of the component Model Context Protocol. The manipulation leads to argument injection. This vulnerability is traded as CVE-2026-39884. It is possible to initiate the attack remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Flux159 mcp-server-kubernetes up to 3.4.x. It has been rated as critical. This issue affects the function spawn of the file src/tools/port_forward.ts of the component Model Context Protocol. The manipulation with an unknown input leads to a argument injection vulnerability. Using CWE to declare the problem leads to CWE-88. The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

mcp-server-kubernetes is a Model Context Protocol server for Kubernetes cluster management. Versions 3.4.0 and prior contain an argument injection vulnerability in the port_forward tool in src/tools/port_forward.ts, where a kubectl command is constructed via string concatenation with user-controlled input and then naively split on spaces before being passed to spawn(). Unlike all other tools in the codebase which correctly use array-based argument passing with execFileSync(), port_forward treats every space in user-controlled fields (namespace, resourceType, resourceName, localPort, targetPort) as an argument boundary, allowing an attacker to inject arbitrary kubectl flags. This enables exposure of internal Kubernetes services to the network by injecting --address=0.0.0.0, cross-namespace targeting by injecting additional -n flags, and indirect exploitation via prompt injection against AI agents connected to the MCP server. This issue has been fixed in version 3.5.0.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-39884 since 04/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

Upgrading to version 3.5.0 eliminates this vulnerability.

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Productinfo

Type

• Virtualization Software

Vendor

• Flux159

Name

• mcp-server-kubernetes

Version

• 3.0
• 3.1
• 3.2
• 3.3
• 3.4

Website

• Product: https://github.com/Flux159/mcp-server-kubernetes/

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