Fix JWT Vulnerabilities (Weak Signing, None Algo) in Revel
JWT implementation in Revel often relies on external libraries like golang-jwt. If you're not explicitly validating the 'alg' header, an attacker can swap 'HS256' for 'none' or use a public key as an HMAC secret to forge tokens. This guide hardens Revel against these common bypasses.
The Vulnerable Pattern
func (c App) Auth() revel.Result {
tokenString := c.Request.Header.Get("Authorization")
// VULNERABLE: No algorithm validation and hardcoded weak secret
token, _ := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
return []byte("secret123"), nil
})
if token.Valid {
return c.RenderJSON(token.Claims)
}
return c.Forbidden()
}The Secure Implementation
The fix implements two critical defenses: 1. Algorithm Verification: By checking if token.Method is an instance of *jwt.SigningMethodHMAC, we prevent 'alg: none' attacks and 'Key Confusion' attacks where an RSA public key is treated as an HMAC secret. 2. Configuration Injection: Instead of a hardcoded string, we pull the secret from Revel's app.conf, ensuring high-entropy keys can be managed via environment variables.
func (c App) Auth() revel.Result { tokenString := c.Request.Header.Get("Authorization") secret := revel.Config.StringDefault("app.secret", "") if secret == "" { panic("Secret not set") }token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) { // SECURE: Explicitly validate the signing method if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok { return nil, fmt.Errorf("Unexpected signing method: %v", token.Header["alg"]) } return []byte(secret), nil }) if err != nil || !token.Valid { return c.RenderError(fmt.Errorf("Unauthorized")) } return c.RenderJSON(token.Claims)
}
Your Revel API
might be exposed to JWT Vulnerabilities (Weak Signing, None Algo)
74% of Revel apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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