# Improper Handling of Unicode Encoding (CWE-176)

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

**Stack:** JavaScript

- Prevalence: Średnia Pokryto 3 języków
- Impact: Średni Zalecany przegląd
- Prevention: Udokumentowane 3 przykładów poprawek

**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

Strategie zapobiegania dla Improper Handling of Unicode oparte na 1 regułach detekcji Shoulder.

### JavaScript

Normalize Unicode strings with NFKC before security-sensitive comparisons

## Warning Signs

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

## Consequences

- Obejście mechanizmu ochrony
- Wykonanie nieautoryzowanego kodu

## Mitigations

- Normalizuj dane wejściowe Unicode do postaci kanonicznej przed przetwarzaniem
- Kontrole bezpieczeństwa stosuj po normalizacji Unicode
- Stosuj funkcje porównujące świadome Unicode

## 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 a
  - 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 a
  - 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