# Language-Specific Vulnerability Patterns

CORRECT/WRONG code examples for common vulnerabilities in Bitwarden's stack. Consult these when reviewing code or recommending fixes.

## C# / .NET

```csharp
// WRONG — SQL injection via string concatenation
var query = $"SELECT * FROM Users WHERE Id = '{userId}'";
var result = connection.Execute(query);

// CORRECT — parameterized query
var query = "SELECT * FROM Users WHERE Id = @UserId";
var result = connection.Execute(query, new { UserId = userId });
```

```csharp
// WRONG — insecure deserialization with type handling
JsonConvert.DeserializeObject<object>(input, new JsonSerializerSettings {
    TypeNameHandling = TypeNameHandling.All
});

// CORRECT — no type name handling on untrusted input
JsonConvert.DeserializeObject<ExpectedType>(input);
```

```csharp
// WRONG — path traversal via user input
var filePath = Path.Combine(baseDir, userInput);
var content = File.ReadAllText(filePath);

// CORRECT — canonicalize and validate
var filePath = Path.GetFullPath(Path.Combine(baseDir, userInput));
if (!filePath.StartsWith(Path.GetFullPath(baseDir)))
    throw new UnauthorizedAccessException();
var content = File.ReadAllText(filePath);
```

```csharp
// WRONG — SSRF via user-controlled URL
var response = await httpClient.GetAsync(userProvidedUrl);

// CORRECT — validate against allowlist
var uri = new Uri(userProvidedUrl);
if (!AllowedHosts.Contains(uri.Host))
    throw new ArgumentException("Host not allowed");
var response = await httpClient.GetAsync(uri);
```

```csharp
// WRONG — XXE via default XML settings
var doc = new XmlDocument();
doc.LoadXml(userInput);

// CORRECT — disable DTD and external entities
var doc = new XmlDocument();
doc.XmlResolver = null;
doc.LoadXml(userInput);
```

## TypeScript / Angular

```typescript
// WRONG — XSS via innerHTML
element.innerHTML = userInput;

// CORRECT — use framework text binding
// In Angular templates: {{ userInput }} (auto-escaped)
// Or use DomSanitizer with explicit trust only for known-safe content
```

```typescript
// WRONG — bypassing Angular security without justification
this.sanitizer.bypassSecurityTrustHtml(userInput);

// CORRECT — only bypass for content fully controlled by the application
const trustedContent = this.generateSafeHtml(); // no user input
this.sanitizer.bypassSecurityTrustHtml(trustedContent);
```

```typescript
// WRONG — open redirect
window.location.href = params.get("redirect");

// CORRECT — validate redirect target
const redirect = params.get("redirect");
const url = new URL(redirect, window.location.origin);
if (url.origin !== window.location.origin) {
  throw new Error("Invalid redirect");
}
window.location.href = url.toString();
```

```typescript
// WRONG — insecure postMessage (no origin check)
window.addEventListener("message", (event) => {
  processData(event.data);
});

// CORRECT — validate origin
window.addEventListener("message", (event) => {
  if (event.origin !== "https://expected-origin.com") return;
  processData(event.data);
});
```

## SQL

```sql
-- WRONG — dynamic SQL with concatenation
EXECUTE('SELECT * FROM Users WHERE Name = ''' + @Name + '''');

-- CORRECT — parameterized dynamic SQL
EXECUTE sp_executesql N'SELECT * FROM Users WHERE Name = @Name', N'@Name NVARCHAR(100)', @Name = @Name;
```