Arp Spoofing with Jwt Tokens

Arp Spoofing attacks targeting JWT tokens typically occur when an attacker positions themselves between a client and server on the same network segment. The attacker uses ARP poisoning to intercept network traffic, then specifically targets JWT tokens in transit. Unlike generic ARP spoofing, JWT-focused attacks exploit the stateless nature of JWTs and their common transmission patterns.

The most common JWT ARP spoofing scenario involves intercepting Authorization headers containing Bearer tokens. When a client sends a request like Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..., the attacker captures this token before it reaches the intended server. Since JWTs are often used without additional transport-layer protections beyond HTTPS, successful ARP spoofing can expose these tokens.

Another manifestation occurs with JWT refresh tokens. Many applications store long-lived refresh tokens in HTTP-only cookies, but some implementations transmit them in URLs or less secure headers. An ARP spoofing attack can capture these refresh tokens, allowing the attacker to obtain new access tokens indefinitely. This is particularly dangerous because refresh tokens typically have longer expiration times than access tokens.

Attackers may also target JWTs in API responses. When APIs return JWTs in response bodies or custom headers, ARP spoofing can capture these tokens before they reach the client. This is especially problematic in microservices architectures where JWTs are passed between services, creating multiple interception points.

The stateless nature of JWTs makes them vulnerable in ARP spoofing scenarios. Once captured, a valid JWT can be used until expiration without requiring further interaction with the issuing server. This contrasts with session-based authentication where server-side session invalidation can provide some protection against captured credentials.

Detecting ARP spoofing vulnerabilities in JWT implementations requires examining both network transmission patterns and token handling practices. Network-level detection involves monitoring for ARP traffic anomalies, but JWT-specific detection focuses on token exposure points.

Key detection areas include:

• Token transmission over non-HTTPS channels - JWTs sent over HTTP are immediately vulnerable to ARP spoofing
• Token inclusion in URLs - query parameters can appear in browser history, logs, and are easily intercepted
• Weak token encryption - JWTs using HS256 with weak secrets are vulnerable even if intercepted
• Missing token rotation - tokens that never refresh give attackers longer windows of exploitation

Using middleBrick's API security scanner, you can identify JWT-specific ARP spoofing vulnerabilities by scanning your API endpoints. The scanner tests for tokens transmitted in insecure ways, examines JWT signature algorithms, and checks for proper HTTPS enforcement. middleBrick's black-box approach simulates an attacker's perspective, testing your unauthenticated attack surface for JWT exposure.

The scanner specifically looks for:

• Authorization headers containing Bearer tokens transmitted over HTTP
• JWTs in URL query parameters or path segments
• Response bodies containing JWTs without proper transport security
• Weak JWT signature algorithms (HS256 with short keys, none algorithm)
• Missing HTTPS enforcement on token endpoints

middleBrick's LLM security module also checks for AI-specific JWT vulnerabilities, such as tokens embedded in system prompts or exposed through AI endpoint responses, which could be captured through ARP spoofing in development environments.

Securing JWTs against ARP spoofing requires a defense-in-depth approach combining transport security, token design, and implementation practices. The foundation is always HTTPS everywhere - never transmit JWTs over HTTP, regardless of the network environment.

For token design, implement these JWT-specific protections:

// Secure JWT generation with proper claims and rotation
const generateSecureJWT = (payload, secret) => {
  const token = jwt.sign({
  return token;
};

Key remediation steps:

1. Always use RS256 or ES256 algorithms - avoid HS256 which relies on shared secrets that can be compromised through ARP spoofing
2. Implement short-lived access tokens - 5-15 minutes reduces the window of opportunity for captured tokens
3. Use refresh tokens with rotating refresh patterns - each refresh returns a new refresh token, invalidating the previous one
4. Store tokens securely - use HTTP-only, secure cookies for refresh tokens; avoid localStorage for JWTs
5. Implement token revocation capabilities - maintain a token blacklist or use JWT ID (jti) claims for selective invalidation

Here's a secure refresh token implementation:

// Secure refresh token endpoint
app.post('/refresh', async (req, res) => {
  try {
    const decoded = jwt.verify(refreshToken, REFRESH_SECRET);
    if (!user || user.tokenVersion !== decoded.tokenVersion) {
    // Rotate refresh token
    res.cookie('refreshToken', newRefreshToken, { httpOnly: true, secure: true, sameSite: 'strict' });

Additional protections include implementing IP binding for JWTs (storing client IP in token claims and validating on each request), using audience (aud) and issuer (iss) claims to restrict token usage, and implementing rate limiting on token endpoints to slow down potential attacks.