Improper Verification of Cryptographic Signature (CWE-347)

Improper Verification of Cryptographic Signature

The product does not verify, or incorrectly verifies, the cryptographic signature for data.

Cryptographic signatures are used to verify the authenticity and integrity of data. When signature verification is missing or incorrectly implemented, attackers can forge or tamper with data.

Prevalence

High

Frequently exploited

Impact

Critical

1 critical-severity rules

Prevention

Documented

4 fix examples

2 Prevention

How to fix this vulnerability

Prevention strategies for Improper Signature Verification based on 4 Shoulder detection rules.

🐍 Python View all Python details →

FastAPI JWT Security Issues HIGH

Load JWT secret from environment and explicitly specify allowed algorithms

+11 -6 python

- from jose import jwt
- 
- SECRET = "my-secret-key"
- 
- def decode_token(token: str):
-     return jwt.decode(token, SECRET)
+ from pydantic_settings import BaseSettings
+ from jose import jwt
+ 
+ class Settings(BaseSettings):
+     SECRET_KEY: str
+     ALGORITHM: str = "HS256"
+ 
+ settings = Settings()
+ 
+ def decode_token(token: str):
+     return jwt.decode(token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM])

JWT Algorithm Confusion Attack CRITICAL

Always specify allowed algorithms explicitly when decoding JWT tokens

+13 -7 python

  import jwt
- from flask import request
- 
- @app.route('/api/user')
- def get_user():
-     token = request.headers.get('Authorization')
-     payload = jwt.decode(token, SECRET_KEY, verify=False)
-     return {'user': payload['user_id']}
+ import os
+ from flask import request
+ 
+ SECRET_KEY = os.environ['JWT_SECRET']
+ 
+ @app.route('/api/user')
+ def get_user():
+     token = request.headers.get('Authorization')
+     try:
+         payload = jwt.decode(token, SECRET_KEY, algorithms=['HS256'])
+         return {'user': payload['user_id']}
+     except jwt.InvalidTokenError:
+         return {'error': 'Invalid token'}, 401

🐹 Go View all Go details →

JWT Security Vulnerabilities HIGH

Validate JWT algorithm explicitly, use strong secrets, and set expiration

+4 -1 go

  func parseToken(tokenString string) (*jwt.Token, error) {
      return jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
-         return []byte("secret"), nil
+         if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
+             return nil, fmt.Errorf("unexpected method: %v", token.Header["alg"])
+         }
+         return []byte(os.Getenv("JWT_SECRET")), nil
      })
  }

🟨 JavaScript View all JavaScript details →

JWT Decode Without Verification HIGH

Use jwt.verify() instead of jwt.decode() to validate token signatures

+3 -1 javascript

- const decoded = jwt.decode(token);
+ const decoded = jwt.verify(token, process.env.JWT_SECRET, {
+   algorithms: ['RS256']
+ });
  req.user = decoded;

Key Practices

Use of jwt

3 Detection

Find vulnerabilities in your code

Use Shoulder to scan your codebase for Improper Verification of Cryptographic Signature patterns. 4 rules.

terminal

# Scan with Shoulder CLI
npx @shoulderdev/cli trust --cwe=347

# Or scan entire project
npx @shoulderdev/cli trust .

Detection Rules (4)

🐍 Python 2 rules

FastAPI JWT Security Issues HIGH

Detects JWT security issues in FastAPI applications including: - Weak or hardcoded secrets - Missing algorithm verification - Insufficient token validation - Insecure token storage patterns

JWT Algorithm Confusion Attack CRITICAL

Detects JWT tokens decoded without algorithm verification or accepting the 'none' algorithm, allowing token forgery.

🐹 Go 1 rules

JWT Security Vulnerabilities HIGH

JWT allows "none" algorithm, uses weak secret, or lacks expiration.

🟨 Javascript 1 rules

JWT Decode Without Verification HIGH

Detects use of jwt.decode() without proper verification, leading to authentication bypass. jwt.decode() decodes a JWT token WITHOUT verifying its signature. This means an attacker can create a token with any payload they want, and the application will trust it. Common mistakes: - Using jwt.decode() instead of jwt.verify() - Decoding token for inspection then trusting the payload - Using decoded payload for authorization decisions The decoded payload should NEVER be trusted for security decisions without verification.

🔷 Typescript 1 rules

JWT Decode Without Verification HIGH

4 Warning Signs

What to watch for in code reviews

These patterns indicate potential Improper Verification of Cryptographic Signature vulnerabilities. Look for these during code reviews and security audits.

🟠

JWT implementation has security vulnerabilities fastapi-jwt-security

🟠

JWT security issues in FastAPI applications including: - Weak or hardcoded secrets - Missing algorit fastapi-jwt-security

🟠

use of jwt javascript-jwt-decode-without-verify

🔴

JWT tokens decoded without algorithm verification or accepting the 'none' algorithm, allowing token python-jwt-algorithm-confusion

🔍

Scan your codebase for Improper Verification of Cryptographic Signature

Shoulder CLI finds vulnerable patterns across your entire codebase.

npx shoulder trust Browse all rules