Same Origin Policy bypass in WebKit Navigation API

This repository is a small browser-based proof of concept for CVE-2026-20643 targeting WebKit Navigation API behavior during cross-port navigations. It contains four files: a minimal README referencing the CVE, a standalone demonstration page (index.html), a more formal test case (navigate-event-canintercept-cross-port.html), and a bundled WebKit/WPT-style reporting helper (resources/testharnessreport.js). The core capability is not remote code execution or payload delivery; instead, it exercises a browser security boundary condition. Both HTML files compute the current port, switch to a different port on the same hostname (8000 <-> 8800), build a target URL, register a 'navigate' event listener on the Navigation API, trigger navigation by programmatically clicking an anchor, and inspect event.canIntercept. Correct behavior is that canIntercept must be false for cross-port navigations. The standalone page logs the observed value to the DOM and console, while the test-harness page asserts the expected value and resolves a promise after preventing the navigation. The repository structure suggests a vulnerability reproduction and regression-test setup rather than a weaponized exploit. index.html is the easiest manual entry point for reproducing the issue in a browser. navigate-event-canintercept-cross-port.html is a more formal automated test suitable for browser testing environments. resources/testharnessreport.js is generic support code for WebKit test execution and result formatting; it is not exploit logic itself, though it references test environment ports 8800 and 9443. No hardcoded external domains or IPs are contacted. The only network target is a dynamically generated same-host URL on a different port, making the exploit behavior dependent on how the page is served. Overall, this is a focused PoC/regression test for a browser-side cross-port navigation interception flaw in WebKit.