# Improper Verification of Cryptographic Signature (CWE-347)

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

**Stack:** Go

- Prevalence: 高 频繁被利用
- Impact: 关键 1 条严重级别为关键的规则
- Prevention: 已记录 4 个修复示例

**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

基于 1 条 Shoulder 检测规则的 Improper Signature Verification 预防策略。

### Go

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

## Warning Signs

- [HIGH] JWT implementation has security weaknesses

## Consequences

- 绕过保护机制
- 执行未授权代码
- 修改应用程序数据

## Mitigations

- 在信任数据之前始终验证签名
- 对签名验证使用经过充分测试的加密库
- 对 JWT,始终验证签名并校验算法

## 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