# Null Byte Interaction Error (Poison Null Byte) (CWE-626)

The product does not properly handle null bytes or NUL characters when passing data to other components.

- Prevalence: Medium 1 language covered
- Impact: High 1 high-severity rules
- Prevention: Documented 1 fix examples

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

## Description

Null byte injection can be used to truncate strings and bypass security checks. For example, a filename check might be bypassed by appending a null byte followed by a different extension.

## Prevention

### Python

Remove null bytes and use secure_filename() for user-provided filenames

## Warning Signs

- [HIGH] file operations that may be vulnerable to null byte injection

## Consequences

- Bypass Protection Mechanism
- Execute Unauthorized Code

## Mitigations

- Remove or reject null bytes from input
- Use functions that handle null bytes properly
- Validate input after null byte removal

## Detection

- Total rules: 1
- Languages: python

## Rules by Language

### Python (1 rules)

- **Null Byte Injection** [HIGH]: Detects file operations that may be vulnerable to null byte injection.
  - Remediation: Remove null bytes and use secure_filename() for user-provided filenames.

```python
from werkzeug.utils import secure_filename
safe_name = secure_filename(filename.replace('\x00', ''))
```

Learn more: https://shoulder.dev/learn/python/cwe-626/null-byte-injection