# Improper Verification of Cryptographic Signature (CWE-347)

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

**Stack:** Go

- Prevalence: High Frequently exploited
- Impact: Critical 1 critical-severity rules
- Prevention: Documented 4 fix examples

**OWASP:** Cryptographic Failures (A02:2021-Cryptographic Failures) - #2

## Description

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.

## Prevention

Prevention strategies for Improper Signature Verification based on 1 Shoulder detection rules.

### Go

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

## Warning Signs

- [HIGH] JWT implementation has security weaknesses

## Consequences

- Bypass Protection Mechanism
- Execute Unauthorized Code
- Modify Application Data

## Mitigations

- Always verify signatures before trusting data
- Use well-tested cryptographic libraries for signature verification
- For JWT, always verify the signature and validate the algorithm

## Detection

- Total rules: 4
- Critical: 1
- Languages: python, go, javascript, typescript

## Rules by Language

### Go (1 rules)

- **JWT Security Vulnerabilities** [HIGH]: JWT allows "none" algorithm, uses weak secret, or lacks expiration.
  - Remediation: Validate algorithm explicitly and set token expiration.

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

Learn more: https://shoulder.dev/learn/go/cwe-347/jwt-vulnerabilities