# Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting') (CWE-113)

The product receives data from an HTTP agent/component, and it places this data in HTTP response headers without neutralizing CRLF sequences.

**Stack:** Python

- Prevalence: 中 3 言語をカバー
- Impact: ハイ 2 件の重大度ハイのルール
- Prevention: 文書化済み 3 件の修正例

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

## Description

An attacker can inject CRLF sequences into HTTP headers to create additional headers or response body content. This can lead to cache poisoning, cross-site scripting, or other attacks.

## Prevention

1 件の Shoulder 検出ルールに基づく HTTP Response Splitting の予防策。

### Python

Strip CRLF characters from user input before using in HTTP headers

## Warning Signs

- [HIGH] user input flowing into HTTP response headers without CRLF
sanitization

## Consequences

- 未承認コードの実行
- 保護メカニズムの回避
- アプリケーションデータの変更

## Mitigations

- HTTP レスポンスヘッダーにユーザー入力を直接含めない
- ヘッダーに含まれる可能性のあるユーザー入力をすべてサニタイズする
- エンコードを処理するフレームワーク提供のヘッダー設定メソッドを使用する

## Detection

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

## Rules by Language

### Python (1 rules)

- **HTTP Header Injection** [HIGH]: Detects user input flowing into HTTP response headers without CRLF
sanitization.
  - Remediation: Remove CRLF characters from header values.

```python
import re
safe_value = re.sub(r'[\r\n]', '', user_value)
```

Learn more: https://shoulder.dev/learn/python/cwe-113/header-injection