CVE-2026-40576
Published: 21 April 2026
Summary
CVE-2026-40576 is a critical-severity Path Traversal (CWE-22) vulnerability. Its CVSS base score is 9.4 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 19.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
This vulnerability is AI-related — categorised as AI Agent Protocols and Integrations; in the Protocol-Specific Risks risk domain.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-10 (Information Input Validation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Validates crafted filepath arguments to MCP tool handlers, preventing path traversal by ensuring inputs conform to expected directory confinement.
Enforces approved access to filesystem resources, directly addressing the get_excel_path() failure to check absolute paths and validate relative paths against EXCEL_FILES_PATH.
Monitors and controls network communications to the server bound to 0.0.0.0 by default, restricting unauthenticated remote access required for exploitation.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Path traversal in network-exposed unauthenticated server directly enables remote exploitation of public-facing application (T1190); explicit arbitrary file read facilitates data collection from local system (T1005); arbitrary file write facilitates ingress of tools/files (T1105).
NVD Description
excel-mcp-server is a Model Context Protocol server for Excel file manipulation. A path traversal vulnerability exists in excel-mcp-server versions up to and including 0.1.7. When running in SSE or Streamable-HTTP transport mode (the documented way to use this server remotely),…
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an unauthenticated attacker on the network can read, write, and overwrite arbitrary files on the host filesystem by supplying crafted filepath arguments to any of the 25 exposed MCP tool handlers. The server is intended to confine file operations to a directory set by the EXCEL_FILES_PATH environment variable. The function responsible for enforcing this boundary — get_excel_path() — fails to do so due to two independent flaws: it passes absolute paths through without any check, and it joins relative paths without resolving or validating the result. Combined with zero authentication on the default network-facing transport and a default bind address of 0.0.0.0 (all interfaces), this allows trivial remote exploitation. This vulnerability is fixed in 0.1.8.
Deeper analysisAI
CVE-2026-40576 is a path traversal vulnerability (CWE-22) in the excel-mcp-server, a Model Context Protocol server designed for Excel file manipulation. The issue affects versions up to and including 0.1.7, specifically when the server is running in SSE or Streamable-HTTP transport mode, which is the documented method for remote usage. The vulnerability stems from flaws in the get_excel_path() function, which fails to properly enforce confinement to the directory specified by the EXCEL_FILES_PATH environment variable: it allows absolute paths to pass unchecked and joins relative paths without resolution or validation. This results in a CVSS v3.1 base score of 9.4 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H).
An unauthenticated attacker on the same network can exploit this vulnerability remotely by supplying crafted filepath arguments to any of the 25 exposed MCP tool handlers. The server binds to 0.0.0.0 (all interfaces) by default with no authentication, enabling trivial exploitation. Successful attacks allow the attacker to read, write, and overwrite arbitrary files on the host filesystem, potentially leading to full compromise depending on the targeted files and server privileges.
The GitHub security advisory (GHSA-j98m-w3xp-9f56) confirms the vulnerability and states that it is fixed in version 0.1.8. Security practitioners should upgrade to 0.1.8 or later, verify the EXCEL_FILES_PATH configuration, and consider restricting network access to the server until patching is complete.
Details
- CWE(s)
AI Security AnalysisAI
- AI Category
- AI Agent Protocols and Integrations
- Risk Domain
- Protocol-Specific Risks
- OWASP Top 10 for LLMs 2025
- None mapped
- Classification Reason
- Matched keywords: mcp, model context protocol, mcp, mcp