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MCP-LOG-02-secret-redaction.md

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title MCP-LOG-02 — Secret Redaction in Logs
weight 62

MCP-LOG-02 — Secret Redaction in Logs

Level: L1
Domain: LOG

Requirement

MCP servers MUST NOT log secrets (API keys, passwords, tokens, credentials) in plaintext. Implement automated redaction or avoid logging sensitive parameters entirely.

Rationale

Logs are often stored insecurely, aggregated in log management systems, and accessible to many personnel. Plaintext secrets in logs enable credential theft.

Scope

All logging (application logs, access logs, error logs).

Required Evidence

  1. Logging configuration or code showing redaction of sensitive fields
  2. Sample log output confirming secrets are redacted (e.g., api_key=***REDACTED***)
  3. Test: tool invoked with API key → log does not contain actual key

Verification Guidance

Static

# Example
import re
SENSITIVE_PATTERNS = [
    r'(api[_-]?key=)([^\s&]+)',
    r'(Authorization:\s*Bearer\s+)([^\s]+)',
    r'(password=)([^\s&]+)'
]

def redact_secrets(message):
    for pattern in SENSITIVE_PATTERNS:
        message = re.sub(pattern, r'\1***REDACTED***', message)
    return message

logger.info(redact_secrets(f"Calling API with {api_key}"))

Dynamic

  • Trigger error with API key in request
  • Check logs: key should not appear

Mappings

  • CWE: CWE-532 (Insertion of Sensitive Information into Log File)
  • OWASP Top 10: A09:2021
  • OWASP MCP Top 10: MCP-01 (Token Mismanagement & Secret Exposure)

Exceptions & Compensating Controls

NOT_APPLICABLE: If server never handles secrets (rare).

References

  • WorkOS: "Best Practices for MCP Secrets Management" (July 2024)
  • Palo Alto Networks: "MCP Security Exposed" (May 2024)
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