wstg-clnt-04

Testing & Quality

Testing for Client-Side URL Redirect

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wstg-clnt-04

Test ID

WSTG-CLNT-04

Test Name

Testing for Client-Side URL Redirect

High-Level Description

Client-side URL redirect vulnerabilities (open redirects) occur when JavaScript redirects users based on URL parameters without validation. Attackers can craft links that redirect victims to malicious sites, facilitating phishing attacks.

What to Check

How to Test

Step 1: Identify Redirect Parameters

#!/bin/bash
TARGET="https://target.com"

# Common redirect parameters
params=("url" "redirect" "next" "return" "returnUrl" "goto" "destination" "redir" "redirect_uri" "continue")

for param in "${params[@]}"; do
    response=$(curl -sI "$TARGET/login?$param=https://evil.com" | grep -i "location")
    if echo "$response" | grep -qi "evil.com"; then
        echo "[VULN] Open redirect via: $param"
    fi
done

Step 2: Test Bypass Techniques

#!/bin/bash
TARGET="https://target.com"
PARAM="redirect"

payloads=(
    "https://evil.com"
    "//evil.com"
    "https://target.com.evil.com"
    "https://evil.com/target.com"
    "https://target.com@evil.com"
    "javascript:alert(1)"
    "//evil.com/%2f%2e%2e"
    "https:evil.com"
    "/\\evil.com"
)

for payload in "${payloads[@]}"; do
    echo "Testing: $payload"
    curl -sI "$TARGET/auth?$PARAM=$payload" | grep -i "location"
done

Step 3: JavaScript Redirect Analysis

// Search for these patterns in JS files:
// location.href =
// location.replace(
// window.location =
// window.open(

// Check if URL parameter is used without validation
const urlParams = new URLSearchParams(window.location.search)
const redirectUrl = urlParams.get("redirect")

// Vulnerable pattern:
window.location.href = redirectUrl // No validation!

// Safe pattern:
const allowedHosts = ["target.com", "sub.target.com"]
try {
  const url = new URL(redirectUrl)
  if (allowedHosts.includes(url.hostname)) {
    window.location.href = redirectUrl
  }
} catch (e) {
  // Invalid URL
}

Remediation

function safeRedirect(url) {
  const allowedHosts = ["example.com", "sub.example.com"]

  try {
    const parsed = new URL(url, window.location.origin)

    // Only allow same-origin or whitelisted hosts
    if (parsed.origin === window.location.origin || allowedHosts.includes(parsed.hostname)) {
      window.location.href = parsed.href
    } else {
      window.location.href = "/" // Default safe redirect
    }
  } catch (e) {
    window.location.href = "/"
  }
}

Risk Assessment

Finding	CVSS	Severity
Open redirect	4.7	Medium
javascript: URI redirect	6.1	Medium

CWE Categories

CWE ID	Title
CWE-601	URL Redirection to Untrusted Site

Checklist

[ ] Redirect parameters identified
[ ] Bypass techniques tested
[ ] JavaScript redirect code analyzed
[ ] javascript: URI tested
[ ] Findings documented