# NULL Pointer Dereference (CWE-476)

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL.

**Stack:** JavaScript

- Prevalence: Mittel 2 Sprachen abgedeckt
- Impact: Mittel Review empfohlen
- Prevention: Dokumentiert 2 Fix-Beispiele

**OWASP:** Insecure Design (A04:2021-Insecure Design) - #4

## Description

NULL pointer dereferences typically cause the application to crash. In some cases, they may be exploitable for denial of service or potentially for code execution.

## Prevention

### JavaScript

Replace non-null assertions (!) with explicit null checks or optional chaining

## Warning Signs

- [LOW] Non-null assertion (!), used on '...' without explicit null/undefined check. This may cause runtime crashes if the value

## Consequences

- DoS: Absturz/Beenden/Neustart

## Mitigations

- Pointer vor dem Dereferenzieren prüfen
- Sprachfeatures nutzen, die Null-Pointer-Probleme vermeiden
- Geeignete Fehlerbehandlung für Null-Rückgaben implementieren

## Detection

- Total rules: 2
- Languages: go, typescript

## Rules by Language

### Typescript (1 rules)

- **Non-Null Assertion Without Null Check** [LOW]: The non-null assertion operator (!) bypasses null/undefined checks at compile time
without runtime safety, causing crashes when values are unexpectedly null.
  - Remediation: Use explicit null checks or optional chaining instead of non-null assertions.

```typescript
function getUserEmail(userId: string) {
  const user = users.find(u => u.id === userId);
  if (!user) {
    throw new Error('User not found');
  }
  return user.email;
}
```

Learn more: https://shoulder.dev/learn/typescript/cwe-476/non-null-assertion