# Improper Restriction of XML External Entity Reference (CWE-611)

The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.

- 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:** Security Misconfiguration (A05:2021-Security Misconfiguration) - #5

## Description

XML External Entity (XXE) attacks exploit features of XML parsers to read local files, perform server-side request forgery, or cause denial of service.

## Prevention

基于 3 条 Shoulder 检测规则的 XML External Entity (XXE) 预防策略。

### Key Practices

- Use denial of service

### Go

Go's encoding/xml is safe by default; reject XML with DOCTYPE declarations as defense in depth

### JavaScript

Disable external entity processing in XML parsers or use JSON instead of XML

### Python

Use defusedxml instead of standard XML parsers for untrusted input

## Warning Signs

- [HIGH] unsafe XML parsing that could allow XML External Entity (XXE) attacks
- [HIGH] XML parsing with external entity processing enabled

## Consequences

- 读取应用程序数据
- 读取文件或目录
- 拒绝服务 (DoS)

## Mitigations

- 在 XML 解析器中禁用外部实体处理
- 尽可能使用 JSON 等更简单的数据格式
- 对 XML 输入进行验证和净化

## Detection

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

## Rules by Language

### Go (1 rules)

- **XML External Entity (XXE) Injection** [HIGH]: User-controlled XML parsed without disabling external entities.
  - Remediation: Go's encoding/xml is safe by default. Reject XML with DOCTYPE declarations.

```go
if bytes.Contains(body, []byte("<!DOCTYPE")) {
    return errors.New("DOCTYPE not allowed")
}
var data MyStruct
xml.Unmarshal(body, &data)
```

Learn more: https://shoulder.dev/learn/go/cwe-611/xxe

### Javascript (1 rules)

- **XML External Entity (XXE) Injection** [HIGH]: Detects unsafe XML parsing that could allow XML External Entity (XXE) attacks.
XXE can lead to file disclosure, SSRF, denial of service, and other attacks.
  - Remediation: Disable external entity processing or use JSON instead of XML.

```javascript
const { XMLParser } = require('fast-xml-parser');
const parser = new XMLParser({ processEntities: false });
const result = parser.parse(xmlData);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-611/xxe

### Typescript (1 rules)

- **XML External Entity (XXE) Injection** [HIGH]: Detects unsafe XML parsing that could allow XML External Entity (XXE) attacks.
XXE can lead to file disclosure, SSRF, denial of service, and other attacks.
  - Remediation: Disable external entity processing or use JSON instead of XML.

```javascript
const { XMLParser } = require('fast-xml-parser');
const parser = new XMLParser({ processEntities: false });
const result = parser.parse(xmlData);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-611/xxe

### Python (1 rules)

- **XML External Entity (XXE) Injection** [HIGH]: Detects XML parsing with external entity processing enabled. XXE attacks
allow attackers to read local files, perform SSRF, or cause denial of service.
Always disable external entity processing when parsing untrusted XML.
  - Remediation: Use defusedxml instead of standard XML parsers for untrusted input.

```python
import defusedxml.ElementTree as ET
from flask import request, jsonify

@app.route('/api/xml', methods=['POST'])
def parse_xml():
    try:
        root = ET.fromstring(request.data)
        return jsonify({'name': root.find('name').text})
    except ET.ParseError:
        return jsonify({'error': 'Invalid XML'}), 400
```

Learn more: https://shoulder.dev/learn/python/cwe-611/xxe