GHSA-xh92-rqrq-227v: Mastra Docs MCP Server `@mastra/mcp-docs-server` Leads to Information Exposure
The Mastra Docs MCP Server package `@mastra/mcp-docs-server` is a server designed to provide documentation context to AI agentic workflows, such as those used in AI-powered IDEs.**Resources:**Package URL: [https://www.npmjs.com/package/@mastra/mcp-docs-server](https://www.npmjs.com/package/@mastra/mcp-docs-server)OverviewThe `@mastra/mcp-docs-server` package in versions **0.13.18 and below** is vulnerable to a Directory Traversal attack that results in the disclosure of directory listings. The code contains a security check to prevent path traversal for reading file contents, but this check is effectively bypassed by subsequent logic that attempts to find directory suggestions. An attacker can leverage this flaw to list the contents of arbitrary directories on the user's filesystem, including the user's home directory, exposing sensitive information about the file system's structure.VulnerabilityThe tool's code attempts to prevent path traversal within the `readMdxContent` function. It correctly checks if the resolved path is within the intended base directory. If the check fails, it logs an error and returns `{ found: false }`.*File: `src/tools/docs.ts`*However, the main `execute` function that calls `readMdxContent` contains a logical flaw. Even when `result.found` is `false`, the code proceeds to call `findNearestDirectory(path, availablePaths)`, which does not perform any path validation. This allows the un-sanitized path to be used for directory listing.*File: `src/tools/docs.ts`*This logical error means the initial security check is rendered ineffective, as the subsequent code path leaks directory information using the malicious path.ExploitationAn attacker can exploit this vulnerability through prompt injection in an AI coding assistant like Cursor IDE, which uses the MCP server. By crafting a prompt that instructs the AI agent to use a traversal path, the attacker can trick the tool into listing directories outside of its intended scope.A malicious prompt could be:This leads to the tool returning a list of directories from the user's home directory, as seen in the LLM's response:This output confirms the successful traversal and listing of the user's home directory contents.Proof of Concept**Configure Cursor IDE**: In the `.cursor/mcp.json` file, define the Mastra MCP server:**Enable the MCP server** within the IDE.**Initiate a new chat** and use the malicious prompt provided above.**Observe the output**, which will contain the directory listing from the root of the user's home directory.Attached screenshot confirming the vulnerability:
<img width="1762" height="1125" alt="image" src="https://github.com/user-attachments/assets/a7b83a7b-f8c9-4ca4-9256-1fc1f689d5ec" />ImpactThe vulnerability exposes the user's file system structure. This **information disclosure (CWE-200)** can reveal the presence of sensitive tools (`.BurpSuite`), configuration files (`.config`), cloud credentials (`.aws/`, `.gcp/`), and private project directories. This information could be invaluable to an attacker for planning further, more targeted attacks.RecommendationIt's recommended to apply the following fixes:**Halt Execution on Failure**: Consider modifying the `execute` function to immediately stop processing a path if the `readMdxContent` function detects a path traversal attempt.**Defense-in-Depth**: Apply the same path validation logic used in `readMdxContent` to the `findNearestDirectory` function to ensure it cannot operate outside the intended base directory.CreditDisclosed by [Liran Tal](https://lirantal.com)
CVSS v3.1: 6.5