Individual skill
exploiting-postmessage-vulnerabilities
Exploiting insecure cross-window messaging where senders use a wildcard targetOrigin (leaking sensitive data) or receivers register message handlers with missing/weak origin validation, enabling sensitive-message theft, DOM XSS, prototype-pollution-to-XSS, SOP bypass via null-origin iframes, and trusted-origin relay/parameter-pollution bridges. Activates when pages call postMessage or addEventListener("message", ...).
internal/tools/skills/data/web-application-security/exploiting-postmessage-vulnerabilities/SKILL.md
Source commit d42f381ad34843e71a42658e5c57290c713e85af
What was checked
- Matches the observed repository HEAD
- Yes
- Scanner rules are current
- Yes
- Repository scan complete
- No
- Skill scan complete
- No
- Observed behavior
- Network or broad shell
- Last checked
- Nov 9, 2026
These are observations at the recorded commit, not a guarantee of safety. Review the source before running it.
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Repository context
- Repository stars (not skill ratings)
- 1,313
- Repository last updated
- Nov 8, 2026
- License
- Apache-2.0
Observed agent integration: No specific integration evidence. Standard SKILL.md installation does not imply verified compatibility.
- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- penetration-testing Declared skill tag
- postmessage Declared skill tag
- dom-xss Declared skill tag
- sop-bypass Declared skill tag
- owasp Declared skill tag
- web-security Declared skill tag
- data Derived category
- security Derived category
- testing Derived category
- security-application Derived category
Files and excerpt
File metadata and permitted, redacted excerpts come from the recorded scan. Source links are pinned to that commit.
Read excerpt
# Exploiting postMessage Vulnerabilities
## When to Use
- During authorized tests of apps using `window.postMessage(...)` and `addEventListener("message", ...)`
- When pages send sensitive data (tokens, OAuth codes, account actions) cross-window
- When a page is iframeable (no `X-Frame-Options` / `frame-ancestors`) and posts with wildcard `*`
- When a receiver does anything sensitive (password change, API call, DOM write) with message data
- When SDKs/pixels/analytics gadgets relay URL params via postMessage on a trusted origin
## Critical: Variants Most Often Missed
Two root causes: (1) sender uses wildcard `targetOrigin='*'`; (2) receiver has missing/weak `event.origin` checks. Enumerate handlers first, then test the matrix:
