# Improper Neutralization of CRLF Sequences ('CRLF Injection') (CWE-93)

The product uses CRLF (carriage return line feed) as a special element, e.g. to separate headers or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

**Stack:** Python

- Prevalence: 中 覆盖 3 种语言
- Impact: 高 3 条严重级别为高的规则
- Prevention: 已记录 3 个修复示例

**OWASP:** Injection (A03:2021-Injection) - #3

## Description

CRLF injection can be used to inject malicious headers in HTTP responses (HTTP response splitting), forge log entries, or manipulate other protocols that use CRLF as a delimiter.

## Prevention

基于 1 条 Shoulder 检测规则的 CRLF Injection 预防策略。

### Python

Strip newline characters from email headers before use

## Warning Signs

- [HIGH] user input used in email headers without newline sanitization

## Consequences

- 修改应用程序数据
- 执行未授权代码
- 隐藏活动

## Mitigations

- 对所有用于头部或日志的输入,剥离或编码 CRLF 序列
- 使用能自动处理头部编码的框架
- 验证输入中不包含意外的控制字符

## Detection

- Total rules: 3
- Languages: go, javascript, typescript, python

## Rules by Language

### Python (1 rules)

- **Email Header Injection** [HIGH]: Detects user input used in email headers without newline sanitization.
  - Remediation: Remove newlines from email headers before use.

```python
safe_subject = subject.replace('\r', '').replace('\n', '')
```

Learn more: https://shoulder.dev/learn/python/cwe-93/email-injection