# HTTP Server CVE Analysis and Security Improvements

## Migration Note (Drogon)

The custom HTTP server previously implemented in `dbal/cpp/src/daemon/server.cpp` has been replaced with **Drogon** to reduce CVE exposure and avoid bespoke HTTP parsing. The findings below apply to the **legacy server** and are retained for historical reference.

## Executive Summary

This document analyzes the HTTP server implementation in `dbal/cpp/src/daemon/server.cpp` against common CVE patterns from 2020-2024. Multiple vulnerabilities have been identified that match patterns from well-known CVEs affecting production HTTP servers.

## CVE Patterns Analyzed

Based on research of recent HTTP server vulnerabilities, we examined:

1. **CVE-2024-22087** - Pico HTTP Server Buffer Overflow
2. **CVE-2024-1135** - Gunicorn Transfer-Encoding Request Smuggling
3. **CVE-2024-40725** - Apache HTTP Server mod_proxy Request Smuggling
4. **CVE-2025-55315** - ASP.NET Core Kestrel Request Smuggling
5. **CVE-2024-53868** - Apache Traffic Server Chunked Encoding Flaw
6. **CVE-2022-26377** - Apache HTTP Server AJP Request Smuggling
7. **CVE-2024-23452** - Apache bRPC Request Smuggling

## Identified Vulnerabilities

### 1. Fixed-Size Buffer Overflow Risk (HIGH SEVERITY)
**Location**: `server.cpp:298`
**CVE Pattern**: Similar to CVE-2024-22087

```cpp
char buffer[8192];  // Fixed size buffer
int bytes_read = recv(client_fd, buffer, sizeof(buffer) - 1, 0);
```

**Issue**: 
- Requests larger than 8192 bytes are truncated
- Could lead to incomplete request parsing
- Potential for buffer-related attacks

**Impact**:
- Request truncation may cause parsing errors
- Attackers could craft requests that exploit truncation behavior
- Potential for denial of service

### 2. Request Smuggling - Multiple Content-Length Headers (CRITICAL SEVERITY)
**Location**: `server.cpp:320-346` (parseRequest function)
**CVE Pattern**: Similar to CVE-2024-1135

**Issue**:
- No detection of duplicate Content-Length headers
- Parser accepts last value without validation
- RFC 7230 violation: "If a message is received with both a Transfer-Encoding and a Content-Length header field, the Transfer-Encoding overrides the Content-Length."

**Attack Vector**:
```http
POST /api/status HTTP/1.1
Host: localhost
Content-Length: 6
Content-Length: 100

SMUGGLED_REQUEST_HERE
```

**Impact**:
- Request smuggling attacks
- Cache poisoning
- Session hijacking
- Authentication bypass

### 3. Request Smuggling - Transfer-Encoding Not Supported (HIGH SEVERITY)
**Location**: `server.cpp` (entire parseRequest function)
**CVE Pattern**: Similar to CVE-2024-23452, CVE-2024-53868

**Issue**:
- No handling of Transfer-Encoding header
- No chunked encoding support
- If both Transfer-Encoding and Content-Length are present, both are ignored
- Does not comply with RFC 7230

**Attack Vector**:
```http
POST /api/status HTTP/1.1
Host: localhost
Transfer-Encoding: chunked
Content-Length: 100

0\r\n
\r\n
SMUGGLED_REQUEST
```

**Impact**:
- Request smuggling when behind reverse proxy
- Nginx may interpret differently than this server
- Backend/frontend desynchronization

### 4. No Request Size Limits (HIGH SEVERITY)
**Location**: `server.cpp:298-353`

**Issue**:
- No maximum total request size validation
- No maximum header count validation
- No maximum header size validation
- Allows header bombs and resource exhaustion

**Attack Vector**:
```http
GET /api/status HTTP/1.1
Host: localhost
X-Header-1: value
X-Header-2: value
... (1000s of headers)
```

**Impact**:
- Memory exhaustion
- Denial of service
- Resource consumption

### 5. Integer Overflow in Content-Length (MEDIUM SEVERITY)
**Location**: `server.cpp:342` (implicit in header parsing)

**Issue**:
- No validation of Content-Length value range
- Could overflow when converted to integer
- No maximum body size enforcement

**Attack Vector**:
```http
POST /api/status HTTP/1.1
Host: localhost
Content-Length: 9999999999999999999

```

**Impact**:
- Integer overflow leading to incorrect memory allocation
- Potential buffer overflow
- Denial of service

### 6. CRLF Injection in Headers (MEDIUM SEVERITY)
**Location**: `server.cpp:333-343`

**Issue**:
- Header values not validated for CRLF sequences
- Could allow header injection in logging or forwarding scenarios

**Attack Vector**:
```http
GET /api/status HTTP/1.1
Host: localhost
X-Custom: value\r\nInjected-Header: malicious\r\n
```

**Impact**:
- Log injection
- Header manipulation if headers are forwarded
- Potential for response splitting in certain scenarios

### 7. No Send Timeout (LOW SEVERITY)
**Location**: `server.cpp:269-278`

**Issue**:
- Receive timeout is set (30 seconds)
- Send timeout is not set
- Slow-read attacks possible

**Impact**:
- Resource exhaustion via slow reads
- Connection pool exhaustion
- Denial of service

### 8. Unlimited Thread Creation (HIGH SEVERITY)
**Location**: `server.cpp:264`

**Issue**:
```cpp
std::thread(&Server::handleConnection, this, client_fd).detach();
```

- No limit on concurrent connections
- Each connection spawns a new thread
- Thread exhaustion attack possible

**Impact**:
- Resource exhaustion
- System instability
- Denial of service

### 9. Missing Null Byte Validation (LOW SEVERITY)
**Location**: `server.cpp:320-353`

**Issue**:
- Request path and headers not checked for null bytes
- Could cause issues with C-string functions

**Impact**:
- Potential for path truncation
- Unexpected behavior with certain operations

### 10. No Rate Limiting (MEDIUM SEVERITY)
**Location**: `server.cpp:249-266` (acceptLoop)

**Issue**:
- No connection rate limiting
- No IP-based throttling
- Allows connection flood attacks

**Impact**:
- Connection exhaustion
- Denial of service
- Resource consumption

## Security Improvements Implemented

### 1. Request Size Limits
```cpp
const size_t MAX_REQUEST_SIZE = 65536;      // 64KB max request
const size_t MAX_HEADERS = 100;              // Max 100 headers
const size_t MAX_HEADER_SIZE = 8192;         // 8KB max per header
```

### 2. Content-Length Validation
- Check for duplicate Content-Length headers (reject request)
- Validate Content-Length is a valid number
- Enforce maximum body size limits
- Check for integer overflow

### 3. Transfer-Encoding Detection
- Detect presence of Transfer-Encoding header
- Return 501 Not Implemented for chunked encoding
- Reject requests with both Transfer-Encoding and Content-Length

### 4. CRLF Validation
- Validate header values don't contain CRLF sequences
- Reject requests with header injection attempts

### 5. Null Byte Detection
- Check request path for null bytes
- Check header values for null bytes

### 6. Connection Limits
- Implement thread pool with fixed size
- Track concurrent connections
- Reject new connections when limit reached

### 7. Timeouts
- Add send timeout (30 seconds)
- Keep receive timeout (30 seconds)

### 8. Rate Limiting
- Track connections per IP address
- Implement simple rate limiting
- Block excessive connection attempts

## Testing

A comprehensive security test suite has been created at:
`tests/security/http_server_security_test.cpp`

This suite tests all identified vulnerability patterns and verifies fixes.

### Running Security Tests

```bash
cd dbal/cpp/build
./http_server_security_test
```

## Compliance

After implementing fixes, the server will comply with:
- RFC 7230 (HTTP/1.1 Message Syntax and Routing)
- OWASP HTTP Server Security Guidelines
- CWE-444 (Inconsistent Interpretation of HTTP Requests)
- CWE-119 (Buffer Overflow)
- CWE-400 (Uncontrolled Resource Consumption)

## References

1. [CVE-2024-22087 - Pico HTTP Server Buffer Overflow](https://halcyonic.net/zero-day-research-cve-2024-22087-pico-http-server-in-c-remote-buffer-overflow/)
2. [CVE-2024-1135 - Gunicorn Transfer-Encoding Vulnerability](https://www.cve.news/cve-2024-1135/)
3. [CVE-2024-40725 - Apache HTTP Server Request Smuggling](https://www.techradar.com/pro/vulnerabilities-in-apache-http-server-enable-http-request-smuggling-and-ssl-authentication-bypass)
4. [CVE-2025-55315 - ASP.NET Core Kestrel Smuggling](https://www.microsoft.com/en-us/msrc/blog/2025/10/understanding-cve-2025-55315)
5. [CVE-2024-53868 - Apache Traffic Server Smuggling](https://cybersecuritynews.com/apache-traffic-server-vulnerability/)
6. [RFC 7230 - HTTP/1.1 Message Syntax and Routing](https://tools.ietf.org/html/rfc7230)
7. [OWASP - HTTP Request Smuggling](https://owasp.org/www-community/attacks/HTTP_Request_Smuggling)

## Recommendations

1. **Immediate Action Required**:
   - Implement request smuggling protections (duplicate Content-Length detection)
   - Add request size limits
   - Implement connection pooling with limits

2. **High Priority**:
   - Add Transfer-Encoding handling or explicit rejection
   - Implement send/receive timeouts
   - Add basic rate limiting

3. **Medium Priority**:
   - Add CRLF validation
   - Implement comprehensive logging of security events
   - Add metrics for security monitoring

4. **Long Term**:
   - Consider using a proven HTTP parsing library (e.g., llhttp, http-parser)
   - Add TLS/SSL support
   - Implement authentication/authorization
   - Add Web Application Firewall (WAF) rules

## Conclusion

The current HTTP server implementation has multiple security vulnerabilities that match patterns from known CVEs. While the server is intended for internal use behind nginx, it should still implement proper HTTP parsing and security controls to prevent request smuggling and other attacks.

The identified vulnerabilities range from CRITICAL (request smuggling) to LOW (missing validations). Immediate action should be taken to address the critical and high-severity issues to prevent potential exploitation.
