PostMessage Vulnerabilities Scanner
Identifies insecure postMessage implementations.
What is PostMessage Vulnerabilities?
PostMessage Vulnerabilities occur when window.postMessage() communication lacks proper origin validation or message handling. Attackers can send malicious messages from their domains, and if the receiving page doesn't verify the source or blindly trusts message content, XSS, data theft, or other attacks are possible.
Why is This Important?
PostMessage enables cross-origin communication, making it a critical security boundary. Missing origin checks allow any website to send messages. Common in widget/iframe integrations, OAuth flows, and cross-domain features. Vulnerabilities can expose data or enable XSS across domain boundaries.
How It Works
1. Attack Surface Mapping
Identifies complex attack vectors including race conditions, desync points, and logic flaws in your application.
2. Advanced Exploitation
Executes sophisticated attack techniques that bypass traditional security controls and detection mechanisms.
3. Impact Assessment
Demonstrates real-world impact with detailed exploitation chains and business risk analysis.
Key Capabilities
Expert-level security testing for sophisticated vulnerabilities that evade traditional scanning tools.
- Race condition and timing attack detection
- Request smuggling and desync analysis
- Business logic flaw identification
- Chained exploit development
- Protocol-level vulnerability testing
Frequently Asked Questions
What makes postMessage insecure?
Insecure patterns: not checking event.origin, checking origin with indexOf (bypassable), trusting message data without validation, using eval() or innerHTML on message content, and sending sensitive data with targetOrigin '*'.
How do attackers exploit postMessage?
Attack: host page at evil.com that iframes target.com, send postMessage with malicious payload. If target.com doesn't verify origin, it processes the attacker's message. Or, if legitimate page uses targetOrigin '*', attacker iframe receives sensitive data.
What should origin validation look like?
Secure validation: use exact origin matching (event.origin === 'https://trusted.com'), allowlist specific origins, never use indexOf/startsWith (vulnerable to trusted.com.evil.com), and validate message structure before processing content.
How do I secure postMessage communication?
Prevention: always validate event.origin strictly, specify exact targetOrigin (never '*' for sensitive data), validate message structure and types, sanitize message content before use, use structured clone for complex data, and document expected message formats.
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