TinyWeb is a web server (HTTP, HTTPS) written in Delphi for Win32. Versions prior to version 2.02 are vulnerable to a Denial of Service (DoS) attack known as Slowloris. The server spawns a new OS thread for every incoming connection without enforcing a maximum concurrency limit or an appropriate request timeout. An unauthenticated remote attacker can exhaust server concurrency limits and memory by opening numerous connections and sending data exceptionally slowly (e.g. 1 byte every few minutes). Anyone hosting services using TinyWeb is impacted. Version 2.02 fixes the issue. The patch introduces a CMaxConnections limit (set to 512) and a CConnectionTimeoutSecs idle timeout (set to 30 seconds). As a temporary workaround if upgrading is not immediately possible, consider placing the server behind a robust reverse proxy or Web Application Firewall (WAF) such as nginx, HAProxy, or Cloudflare, configured to buffer incomplete requests and aggressively enforce connection limits and timeouts.
Weakness
The product does not properly control the allocation and maintenance of a limited resource.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Tinyweb | Ritlabs | * | 2.02 (excluding) |
Potential Mitigations
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/147.html
- https://cwe.mitre.org/data/definitions/227.html
- https://cwe.mitre.org/data/definitions/492.html