CVE-2026-39884

OVERVIEW CVE-2026-39884 is an argument injection vulnerability affecting mcp-server-kubernetes versions 3.4.0 and prior. The port_forward tool in src/tools/port_forward.ts constructs kubectl commands through unsafe string concatenation and naive space-based argument splitting, rather than using array-based argument passing like other tools in the codebase. This allows attackers to inject arbitrary kubectl flags through user-controlled fields including namespace, resourceType, resourceName, and port parameters. SEVERITY The vulnerability carries a CVSS 3.1 score of 8.3 (HIGH) with a network-based attack vector, low complexity, and low privilege requirements. Exploitation enables multiple high-impact scenarios including exposure of internal Kubernetes services to external networks via flag injection like --address=0.0.0.0, cross-namespace service targeting through injected flags, and indirect compromise through prompt injection attacks against AI agents utilizing the MCP server. The attack requires only user interaction with no special access, resulting in high confidentiality and integrity impact with some availability risk. EXPLOITATION STATUS The vulnerability is not currently listed on the Known Exploited Vulnerabilities (KEV) catalog and shows no evidence of active exploitation in the wild. The exploit has an extremely low EPSS score of 0.0005, indicating minimal probability of exploitation in real-world conditions. The issue has been remediated in version 3.5.0, and community attention remains limited. Organizations should prioritize patching to the fixed version as a standard maintenance activity rather than treating this as an emergency threat.