# Improper Handling of Unicode Encoding (CWE-176)

The product does not properly handle when an input contains Unicode encoding.

**Stack:** JavaScript

- Prevalence: Medium 3 languages covered
- Impact: Medium Review recommended
- Prevention: Documented 3 fix examples

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

## Description

Unicode characters can have multiple encodings or representations. If an application does not properly handle Unicode, attackers may be able to bypass security filters or cause unexpected behavior using alternate encodings.

## Prevention

Prevention strategies for Improper Handling of Unicode based on 1 Shoulder detection rules.

### JavaScript

Normalize Unicode strings with NFKC before security-sensitive comparisons

## Warning Signs

- [MEDIUM] missing Unicode normalization in security-sensitive string comparisons

## Consequences

- Bypass Protection Mechanism
- Execute Unauthorized Code

## Mitigations

- Normalize Unicode input to a canonical form before processing
- Apply security checks after Unicode normalization
- Use Unicode-aware comparison functions

## Detection

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

## Rules by Language

### Javascript (1 rules)

- **Unicode Normalization Security Issues** [MEDIUM]: Detects missing Unicode normalization in security-sensitive string comparisons.
Unicode allows multiple representations of visually identical characters, which
attackers can exploit to bypass input validation, authentication, or access control.

Common attack vectors:
- Homograph attacks (using lookalike characters): "аdmin" vs "admin" (Cyrillic 'а')
- Case folding differences: "ß" (German sharp s) becomes "SS" when uppercased
- Combining characters: "é" can be a single char or 'e' + combining accent
- Full-width characters: "ａｄｍｉｎ" vs "admin"

Always normalize Unicode strings using String.prototype.normalize() before
security-sensitive comparisons.
  - Remediation: Normalize Unicode strings with NFKC before security-sensitive comparisons:

```javascript
app.post('/login', (req, res) => {
  const username = req.body.username.normalize('NFKC').toLowerCase();
  if (username === 'admin') {
    return res.send('Admin access');
  }
  res.send('User access');
});
```

Learn more: https://shoulder.dev/learn/javascript/cwe-176/unicode-normalization

### Typescript (1 rules)

- **Unicode Normalization Security Issues** [MEDIUM]: Detects missing Unicode normalization in security-sensitive string comparisons.
Unicode allows multiple representations of visually identical characters, which
attackers can exploit to bypass input validation, authentication, or access control.

Common attack vectors:
- Homograph attacks (using lookalike characters): "аdmin" vs "admin" (Cyrillic 'а')
- Case folding differences: "ß" (German sharp s) becomes "SS" when uppercased
- Combining characters: "é" can be a single char or 'e' + combining accent
- Full-width characters: "ａｄｍｉｎ" vs "admin"

Always normalize Unicode strings using String.prototype.normalize() before
security-sensitive comparisons.
  - Remediation: Normalize Unicode strings with NFKC before security-sensitive comparisons:

```javascript
app.post('/login', (req, res) => {
  const username = req.body.username.normalize('NFKC').toLowerCase();
  if (username === 'admin') {
    return res.send('Admin access');
  }
  res.send('User access');
});
```

Learn more: https://shoulder.dev/learn/javascript/cwe-176/unicode-normalization