WebKit Navigation API — Same-Origin Policy bypass via cross-port interception (CVE-2026-20643)

NavigateEvent.canIntercept incorrectly returns true for same-site, cross-port navigations that differ in origin. The interception gate accepts any HTTP-family target after a same-site check without verifying that scheme, host, and port all match. This lets an attacker-controlled page intercept or suppress navigations that should cross an origin boundary.

// WebCore::Navigation::innerDispatchNavigateEvent — 0x1a1303304 (iOS 26.3.1 / 23D8133)

if (!isSameSite && !isSameOrigin)
    return false;
if (targetURL.protocolIsInHTTPFamily())
    return true;  // ← no port/host/scheme component equality check
                  //   cross-port navigations (e.g. :8000 → :8800) slip through

The WebKit mainline fix adds strict per-component equality (scheme / user / password / host / port) before allowing interception.

Serve poc_min.html on port 8000 and open it on an affected device:

python3 -m http.server 8000
# http://127.0.0.1:8000/poc_min.html

Click Run PoC. The page triggers a cross-port navigation (:8000 → :8800) and reports:

Vulnerable:  canIntercept=true
Patched:     canIntercept=false