CVE-2025-56405: Litmus MCP Server Auth Bypass Vulnerability

CVE-2025-56405 Overview

CVE-2025-56405 is an Improper Access Control vulnerability discovered in the litmusautomation litmus-mcp-server through version 0.0.1. This vulnerability allows unauthorized attackers to control the target's MCP (Model Context Protocol) service through the SSE (Server-Sent Events) protocol, potentially enabling complete compromise of the MCP service functionality.

Critical Impact
Unauthorized attackers can gain control over the MCP service through the SSE protocol, potentially leading to data exfiltration, service manipulation, or further compromise of connected systems.

Affected Products

Litmus MCP Server version 0.0.1 and earlier
litmusautomation/litmus-mcp-server implementations using SSE protocol

Discovery Timeline

2025-09-10 - CVE-2025-56405 published to NVD
2025-09-17 - Last updated in NVD database

Technical Details for CVE-2025-56405

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) in the Litmus MCP Server's SSE protocol implementation. The MCP (Model Context Protocol) service lacks proper authentication and authorization mechanisms when handling SSE connections, allowing unauthenticated remote attackers to establish connections and issue commands to the MCP service.

The SSE protocol is designed for real-time server-to-client communication, but in this case, the bidirectional control plane lacks sufficient access restrictions. Attackers exploiting this vulnerability can potentially manipulate the MCP service behavior, intercept sensitive data transmitted through the protocol, or pivot to attack connected automation systems.

The network-based attack vector with no authentication requirements makes this vulnerability particularly concerning for deployments exposed to untrusted networks or the internet.

Root Cause

The root cause is the absence of proper authentication and authorization controls on the SSE endpoint used by the MCP service. The litmus-mcp-server fails to validate the identity and permissions of connecting clients before allowing them to interact with the MCP service through the SSE protocol. This represents a fundamental access control design flaw where security boundaries are not properly enforced at the protocol level.

Attack Vector

The attack can be executed remotely over the network without requiring any authentication or user interaction. An attacker needs only network access to the vulnerable MCP server to establish an SSE connection and begin issuing unauthorized commands to the service.

The exploitation flow involves:

Identifying a vulnerable litmus-mcp-server instance exposed on the network
Establishing an SSE connection to the MCP service endpoint
Sending crafted commands through the SSE protocol to control the MCP service
Extracting sensitive information or manipulating service behavior

For technical details regarding the exploitation mechanism, refer to the GitHub Litmus MCP Server Issue and the GitHub CVE Issue Discussion.

Detection Methods for CVE-2025-56405

Indicators of Compromise

Unexpected SSE connections to the MCP server from unknown or untrusted IP addresses
Anomalous command patterns or unauthorized operations in MCP service logs
Unusual data exfiltration patterns through SSE connections
Authentication bypass attempts or missing authentication headers in connection logs

Detection Strategies

Monitor network traffic for unauthorized SSE connections to the MCP server port
Implement logging and alerting for all MCP service control operations
Deploy network segmentation to limit exposure and establish baseline traffic patterns
Use intrusion detection systems to identify suspicious SSE protocol activity

Monitoring Recommendations

Enable verbose logging on the litmus-mcp-server to capture all connection attempts and commands
Implement network monitoring for anomalous traffic patterns to MCP service endpoints
Configure alerts for connections originating from untrusted network segments
Review MCP service logs regularly for signs of unauthorized access or unusual behavior

How to Mitigate CVE-2025-56405

Immediate Actions Required

Restrict network access to the litmus-mcp-server to trusted IP addresses and network segments only
Implement firewall rules to block external access to MCP service ports
Deploy a reverse proxy with authentication in front of the MCP service
Audit existing deployments for signs of unauthorized access or compromise

Patch Information

At the time of publication, no official patch has been released by Litmus Automation. Organizations should monitor the GitHub Litmus MCP Server repository for security updates and patches. Upgrading to a patched version when available is the recommended long-term remediation.

Workarounds

Implement network-level access controls to restrict SSE connections to authorized clients only
Deploy authentication middleware or a reverse proxy to enforce access control on the MCP service
Isolate the MCP server in a segmented network with restricted access policies
Consider temporarily disabling the SSE protocol if not required for operations until a patch is available

bash

# Example: Restrict access to MCP server using iptables
# Allow only trusted network (e.g., 10.0.0.0/24) to access MCP service port
iptables -A INPUT -p tcp --dport 8080 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP