<!-- Copyright (c) 2026 defconxt. All rights reserved. -->
<!-- Licensed under AGPL-3.0 — see LICENSE file for details. -->
<!-- NERF is a trademark of defconxt. -->
---
name: analyzing-postmessage-security
description: >-
  Analyze postMessage API security including missing origin validation, insecure message handlers, and cross-origin data leakage through window.postMessage communication.
domain: cybersecurity
subdomain: browser-security
tags:
  - postmessage
  - cross-origin
  - origin-validation
  - dom
version: "1.0"
author: defconxt
license: AGPL-3.0
metadata:
  mitre-attack: ["T1059.007"]
  frameworks: ["MITRE ATT&CK", "OWASP"]
  tools: ["burpsuite", "devtools", "semgrep"]
---

# Analyzing Postmessage Security

## Overview

Analyze postMessage API security including missing origin validation, insecure message handlers, and cross-origin data leakage through window.postMessage communication.

## Prerequisites

| Tool / Requirement | Details |
|---|---|
| `burpsuite` | Security tooling |
| `devtools` | Security tooling |
| `semgrep` | Security tooling |
| Browser DevTools, Burp Suite, semgrep for static analysis | Environment requirement |

## Quick Reference

```bash
# Quick start commands
node scripts/agent.js --help
semgrep --config 'rules: [{id: pm, pattern: "addEventListener(\"message\", ...)", languages: [javascript]}]' ./src
```

## Workflow

### Step 1: Find postMessage Handlers

```bash
semgrep --config 'rules: [{id: pm, pattern: "addEventListener(\"message\", ...)", languages: [javascript]}]' ./src
```

### Step 2: Test Origin Validation

```bash
node scripts/agent.js test --url https://target.com --origin https://evil.com
```

### Step 3: Exploit Missing Validation

```bash
node scripts/agent.js exploit --url https://target.com --payload '{"action":"admin"}'
```

## Detection

```yaml
title: Postmessage Security Detection
id: fd60f026-c35e-45a9-b200-6b9ba2bb97cb
status: experimental
description: Detects suspicious activity related to analyzing postmessage security techniques in browser security context
logsource:
  category: proxy
  product: windows
detection:
  selection:
    cs_uri_query: "*script*"
  condition: selection
level: medium
tags:
  - attack.t1059.007
  - attack.initial_access
falsepositives:
  - Browser security extensions performing routine URL reputation checks
```


**Detection Opportunities**

| Indicator | Source | Detection Logic |
|---|---|---|
| Postmessage Security Detection | windows/proxy | Sigma rule (medium) |
| ATT&CK Coverage | MITRE ATT&CK | T1059.007 |

## Verification

- **Verify handler analysis**: `node scripts/agent.js analyze --url https://target.com`
- **Confirm origin bypass**: `node scripts/agent.js test --url https://target.com --origin https://evil.com`

## References

- MITRE ATT&CK: T1059.007
- Frameworks: MITRE ATT&CK, OWASP
- Tools: burpsuite, devtools, semgrep
