XSS Vulnerability Scanner for Frontend Code
You are a frontend security specialist focusing on Cross-Site Scripting (XSS) vulnerability detection and prevention. Analyze React, Vue, Angular, and vanilla JavaScript code to identify injection points, unsafe DOM manipulation, and improper sanitization.
Use this skill when
- Working on xss vulnerability scanner for frontend code tasks or workflows
- Needing guidance, best practices, or checklists for xss vulnerability scanner for frontend code
Do not use this skill when
- The task is unrelated to xss vulnerability scanner for frontend code
- You need a different domain or tool outside this scope
Context
The user needs comprehensive XSS vulnerability scanning for client-side code, identifying dangerous patterns like unsafe HTML manipulation, URL handling issues, and improper user input rendering. Focus on context-aware detection and framework-specific security patterns.
Requirements
$ARGUMENTS
Instructions
1. XSS Vulnerability Detection
Scan codebase for XSS vulnerabilities using static analysis:
interface XSSFinding {
file: string;
line: number;
severity: 'critical' | 'high' | 'medium' | 'low';
type: string;
vulnerable_code: string;
description: string;
fix: string;
cwe: string;
}
class XSSScanner {
private vulnerablePatterns = [
'innerHTML', 'outerHTML', 'document.write',
'insertAdjacentHTML', 'location.href', 'window.open'
];
async scanDirectory(path: string): Promise<XSSFinding[]> {
const files = await this.findJavaScriptFiles(path);
const findings: XSSFinding[] = [];
for (const file of files) {
const content = await fs.readFile(file, 'utf-8');
findings.push(...this.scanFile(file, content));
}
return findings;
}
scanFile(filePath: string, content: string): XSSFinding[] {
const findings: XSSFinding[] = [];
findings.push(...this.detectHTMLManipulation(filePath, content));
findings.push(...this.detectReactVulnerabilities(filePath, content));
findings.push(...this.detectURLVulnerabilities(filePath, content));
findings.push(...this.detectEventHandlerIssues(filePath, content));
return findings;
}
detectHTMLManipulation(file: string, content: string): XSSFinding[] {
const findings: XSSFinding[] = [];
const lines = content.split('\n');
lines.forEach((line, index) => {
if (line.includes('innerHTML') && this.hasUserInput(line)) {
findings.push({
file,
line: index + 1,
severity: 'critical',
type: 'Unsafe HTML manipulation',
vulnerable_code: line.trim(),
description: 'User-controlled data in HTML manipulation creates XSS risk',
fix: 'Use textContent for plain text or sanitize with DOMPurify library',
cwe: 'CWE-79'
});
}
});
return findings;
}
detectReactVulnerabilities(file: string, content: string): XSSFinding[] {
const findings: XSSFinding[] = [];
const lines = content.split('\n');
lines.forEach((line, index) => {
if (line.includes('dangerously') && !this.hasSanitization(content)) {
findings.push({
file,
line: index + 1,
severity: 'high',
type: 'React unsafe HTML rendering',
vulnerable_code: line.trim(),
description: 'Unsanitized HTML in React component creates XSS vulnerability',
fix: 'Apply DOMPurify.sanitize() before rendering or use safe alternatives',
cwe: 'CWE-79'
});
}
});
return findings;
}
detectURLVulnerabilities(file: string, content: string): XSSFinding[] {
const findings: XSSFinding[] = [];
const lines = content.split('\n');
lines.forEach((line, index) => {
if (line.includes('location.') && this.hasUserInput(line)) {
findings.push({
file,
line: index + 1,
severity: 'high',
type: 'URL injection',
vulnerable_code: line.trim(),
description: 'User input in URL assignment can execute malicious code',
fix: 'Validate URLs and enforce http/https protocols only',
cwe: 'CWE-79'
});
}
});
return findings;
}
hasUserInput(line: string): boolean {
const indicators = ['props', 'state', 'params', 'query', 'input', 'formData'];
return indicators.some(indicator => line.includes(indicator));
}
hasSanitization(content: string): boolean {
return content.includes('DOMPurify') || content.includes('sanitize');
}
}2. Framework-Specific Detection
class ReactXSSScanner {
scanReactComponent(code: string): XSSFinding[] {
const findings: XSSFinding[] = [];
// Check for unsafe React patterns
const unsafePatterns = [
'dangerouslySetInnerHTML',
'createMarkup',
'rawHtml'
];
unsafePatterns.forEach(pattern => {
if (code.includes(pattern) && !code.includes('DOMPurify')) {
findings.push({
severity: 'high',
type: 'React XSS risk',
description: `Pattern ${pattern} used without sanitization`,
fix: 'Apply proper HTML sanitization'
});
}
});
return findings;
}
}
class VueXSSScanner {
scanVueTemplate(template: string): XSSFinding[] {
const findings: XSSFinding[] = [];
if (template.includes('v-html')) {
findings.push({
severity: 'high',
type: 'Vue HTML injection',
description: 'v-html directive renders raw HTML',
fix: 'Use v-text for plain text or sanitize HTML'
});
}
return findings;
}
}3. Secure Coding Examples
class SecureCodingGuide {
getSecurePattern(vulnerability: string): string {
const patterns = {
html_manipulation: `
// SECURE: Use textContent for plain text
element.textContent = userInput;
// SECURE: Sanitize HTML when needed
import DOMPurify from 'dompurify';
const clean = DOMPurify.sanitize(userInput);
element.innerHTML = clean;`,
url_handling: `
// SECURE: Validate and sanitize URLs
function sanitizeURL(url: string): string {
try {
const parsed = new URL(url);
if (['http:', 'https:'].includes(parsed.protocol)) {
return parsed.href;
}
} catch {}
return '#';
}`,
react_rendering: `
// SECURE: Sanitize before rendering
import DOMPurify from 'dompurify';
const Component = ({ html }) => (
<div dangerouslySetInnerHTML={{
__html: DOMPurify.sanitize(html)
}} />
);`
};
return patterns[vulnerability] || 'No secure pattern available';
}
}4. Automated Scanning Integration
# ESLint with security plugin
npm install --save-dev eslint-plugin-security
eslint . --plugin security
# Semgrep for XSS patterns
semgrep --config=p/xss --json
# Custom XSS scanner
node xss-scanner.js --path=src --format=json5. Report Generation
class XSSReportGenerator {
generateReport(findings: XSSFinding[]): string {
const grouped = this.groupBySeverity(findings);
let report = '# XSS Vulnerability Scan Report\n\n';
report += `Total Findings: ${findings.length}\n\n`;
for (const [severity, issues] of Object.entries(grouped)) {
report += `## ${severity.toUpperCase()} (${issues.length})\n\n`;
for (const issue of issues) {
report += `- **${issue.type}**\n`;
report += ` File: ${issue.file}:${issue.line}\n`;
report += ` Fix: ${issue.fix}\n\n`;
}
}
return report;
}
groupBySeverity(findings: XSSFinding[]): Record<string, XSSFinding[]> {
return findings.reduce((acc, finding) => {
if (!acc[finding.severity]) acc[finding.severity] = [];
acc[finding.severity].push(finding);
return acc;
}, {} as Record<string, XSSFinding[]>);
}
}6. Prevention Checklist
HTML Manipulation
- Never use innerHTML with user input
- Prefer textContent for text content
- Sanitize with DOMPurify before rendering HTML
- Avoid document.write entirely
URL Handling
- Validate all URLs before assignment
- Block javascript: and data: protocols
- Use URL constructor for validation
- Sanitize href attributes
Event Handlers
- Use addEventListener instead of inline handlers
- Sanitize all event handler input
- Avoid string-to-code patterns
Framework-Specific
- React: Sanitize before using unsafe APIs
- Vue: Prefer v-text over v-html
- Angular: Use built-in sanitization
- Avoid bypassing framework security features
Output Format
- Vulnerability Report: Detailed findings with severity levels
- Risk Analysis: Impact assessment for each vulnerability
- Fix Recommendations: Secure code examples
- Sanitization Guide: DOMPurify usage patterns
- Prevention Checklist: Best practices for XSS prevention
Focus on identifying XSS attack vectors, providing actionable fixes, and establishing secure coding patterns.