Cyber attacks

Slowloris attack explained in details

In the realm of cybersecurity, various attack techniques have evolved over time, each with its own unique approach and set of challenges. One such technique is the Slowloris attack, a stealthy and efficient method employed by malicious actors to cripple web servers without the need for a massive botnet or heavy network traffic. In this blog post, we will delve into the details of the Slowloris attack, exploring its mechanisms, potential impacts, and how to defend against it.

Understanding the Slowloris Attack

The Slowloris attack, named after the slow-moving nature of a certain type of lizard, is a low-and-slow Denial of Service (DoS) attack designed to exploit a web server’s capacity to handle concurrent connections. Unlike traditional DoS attacks that flood a target server with a high volume of traffic, the Slowloris attack operates differently. It capitalizes on the server’s vulnerability to handling multiple slow, incomplete HTTP requests.

Here’s how the Slowloris attack works:

Persistent Connections: Slowloris initiates multiple connections to the target web server but keeps them open for as long as possible. This is achieved by sending partial HTTP requests to the server and keeping the connection alive by sending occasional header lines, without completing the request.

Resource Starvation: By holding open numerous connections without completing them, Slowloris ties up the server’s resources, such as available threads, memory, and file handles. These resources are essential for handling legitimate incoming requests.

Server Exhaustion: As more connections are established and maintained, the web server becomes overwhelmed, reaching a point where it cannot accept any new incoming connections from legitimate users. This results in a denial of service for genuine clients.

The Stealthy Nature of Slowloris

What makes the Slowloris attack particularly insidious is its ability to remain under the radar. Unlike high-traffic DoS attacks that are easily detectable, Slowloris keeps its resource usage low, making it challenging to distinguish from normal web traffic. It is highly efficient because it requires only a small number of connections to cause significant disruption, and these connections are spread out over time.

Impacts of Slowloris Attack

  • Service Disruption: Slowloris can effectively render a web server unavailable to legitimate users by depleting its capacity to process new requests. This results in service disruption, which can be financially damaging for online businesses.
  • Reputation Damage: Frequent service disruptions due to Slowloris attacks can damage an organization’s reputation, leading to loss of customer trust and potential legal consequences.
  • Increased Operational Costs: Mitigating Slowloris attacks often requires investing in advanced security solutions, server capacity, or DDoS protection services, which can increase operational costs.

Defending Against Slowloris Attacks

To protect your web server from Slowloris attacks, consider implementing the following security measures:

Rate Limiting: Implement rate limiting to restrict the number of concurrent connections from a single IP address. This can help reduce the impact of Slowloris attacks.

Web Application Firewall (WAF): Use a WAF to filter and identify potentially malicious traffic patterns. Modern WAFs can detect Slowloris-like behavior and take actions to mitigate the attack.

Intrusion Detection Systems (IDS): Employ IDS solutions that can identify abnormal traffic patterns indicative of a Slowloris attack and trigger automated responses or alerts.

Keep Software Up-to-Date: Regularly update your web server software and security patches to ensure you are protected against known vulnerabilities.

Load Balancing: Distribute incoming traffic across multiple servers using load balancers. This can help mitigate the impact of Slowloris attacks by spreading the load.


The Slowloris attack is a stealthy and effective technique used by cybercriminals to disrupt web servers without overwhelming them with traffic. Understanding how Slowloris operates and taking proactive steps to defend against it is essential for maintaining the availability and security of web services. By implementing the recommended security measures and staying vigilant, organizations can reduce the risk of falling victim to this subtle yet potentially damaging attack.