What is a Slowloris Attack | How Does a Slowloris Attack Work?
Tags: cybersecurity, dos, security, learning
Published: 2023-12-05 19:22:20

In cybersecurity, Distributed Denial of Service (DDoS) attacks are known for their ability to disrupt the normal functioning of a targeted server, network, or website, rendering it inaccessible to legitimate users. Among the various types of DDoS attacks, one particularly stealthy and insidious variant is the Slowloris attack.

However, unlike other DDoS attacks that flood a target system or network with an overwhelming volume of traffic, the Slowloris attack takes a completely different approach while achieving the same results. 

This article will explore Slowloris attacks as a form of DDOS attacks, how they work, and the impact they can have on an organization.

## What is a Slowloris DDoS Attack
A Slowloris attack is a type of cyber attack that gradually cripples a website or server by sending it a lot of partial requests, keeping these connections open for as long as possible, and eventually causing it to crash or become inaccessible to legitimate users.

Slowloris represents a distinctive approach that exploits the way web servers manage concurrent connections. It accomplishes this by utilizing minimal resources ultimately consuming its capacity to handle further requests.

The Slowloris DDoS technique was initially introduced in 2009 by the prominent security expert Robert "RSnake" Hansen. Its name is inspired by the slow-moving, tree-dwelling sloth, alluding to the gradual and methodical nature of the attack. 

Over the years, Slowloris has been responsible for targeting several high-profile websites, including those of government agencies, financial institutions, and major corporations, causing significant disruption and highlighting the critical need for robust cybersecurity measures.

## How a Slowloris Attack Works
Slowloris functions exploiting the limited resources allocated by the server to each incoming connection, using this constraint to exhaust the server's capacity to handle legitimate requests. The following steps outline the workings of a Slowloris attack:

### Step 1: Initial Connection
The attacker initiates a connection to the target server, but instead of completing the request, it sends partial HTTP headers and keeps the connection open.

### Step 2: Maintaining Open Connections
Slowloris sustains numerous partial connections to the targeted server. By intermittently sending small, meaningless packets or HTTP headers, the attack maintains these connections, preventing the server from timing them out and freeing up resources for new connections.

### Step 3: Resource Exhaustion
As Slowloris continues to occupy the server's available connection slots with these partial connections, it gradually depletes the server's capacity to accept new legitimate connections, thereby leading to a denial of service for genuine users attempting to access the server.

## How to Identify Vulnerable Components in a Server
Servers with limited resources or those configured to allow an excessive number of concurrent connections per IP address are particularly susceptible to Slowloris attacks. Security teams can identify a Slowloris attack through?

1. Using Automated Vulnerability Scanning Tools: Implement automated vulnerability scanning tools that can systematically scan the server's network and applications to detect any existing weaknesses or misconfigurations.
2. Performing Regular Penetration Testing: Conduct periodic penetration testing to simulate potential attack scenarios and identify any exploitable vulnerabilities that could be targeted by malicious actors.
3. Reviewing Web Server Configurations: Analyze the web server's configurations, including connection limits, timeouts, and other settings that can potentially be exploited by Slowloris attacks.
4. Monitoring Resource Utilization: Implement monitoring tools to track the server's resource utilization, such as the number of concurrent connections, to identify any abnormal or suspicious patterns that may indicate a potential vulnerability.
5. Firewall Configuration and Rule Management: Ensure that the firewall is appropriately configured with rules that restrict unauthorized access and filter out potentially malicious traffic, thereby reducing the risk of a successful Slowloris attack.
6. Regular Patch Management: Stay updated with the latest security patches and updates for the server's operating system and all installed applications to address any known vulnerabilities and enhance the overall security posture.

## Impact of Slowloris DDoS Attacks
Slowloris DDoS attacks, with their subtle yet destructive nature, can have far-reaching consequences for the targeted entities, resulting in various adverse impacts that can significantly disrupt normal business operations and tarnish reputations. Some of these effects include:

- Service Disruption: Slowloris attacks lead to a gradual degradation of services, causing legitimate users to experience delays or complete unavailability when trying to access the affected website or server.

![Slowloris attacks can lead to Service Disruption](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/xxawndl2da08dpf3j9dk.png)
- Degraded Performance: The server's performance deteriorates, resulting in sluggish response times, timeouts, and an overall poor user experience, leading to frustration and potential loss of trust among users.
- Loss of Revenue: Extended periods of unavailability or poor performance can result in significant revenue losses for businesses that heavily rely on their online presence for transactions and customer interactions.
- Reputational Damage: Persistent or recurrent Slowloris attacks can undermine the reputation of an organization, eroding customer trust and confidence in the security and reliability of their online services.
- Customer Churn: Dissatisfied customers may seek alternative service providers, leading to a long-term loss of customer base and market share.
- Legal Ramifications: Depending on the severity of the attack and the resulting consequences, affected organizations may face legal liabilities and regulatory sanctions for failing to ensure adequate protection against cyber threats.

## Detection and Prevention of Slowloris Attacks
Effectively identifying and thwarting Slowloris attacks requires a combination of proactive monitoring, robust network security protocols, and diligent mitigation strategies. Implementing comprehensive detection mechanisms and deploying preventive measures can significantly reduce the risk of falling victim to this stealthy form of DDoS attack.

Below are some ways to detect and prevent a Slowloris attack from happening. 

- Real-time Traffic Analysis: Implementing intrusion detection and prevention systems capable of monitoring incoming traffic patterns and identifying unusual connection behavior can help in the early detection of Slowloris attacks.

![Real-time Traffic Analysis](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/afpjktu8xm6z7ix4q1uv.png)
- Behavioral Analysis: Employing anomaly detection tools that analyze the behavior of connections and transactions, specifically focusing on the duration of open connections, can aid in detecting potential Slowloris activities.
- Web Server Configuration Optimization: Configuring web servers to limit the number of concurrent connections per IP address can reduce the susceptibility to Slowloris attacks.
- Implementation of Timeouts and Connection Limits: Setting shorter timeout periods for idle connections and enforcing strict connection limits can help prevent attackers from exploiting the server's resources through prolonged partial connections.
- Traffic Scrubbing Services and DDoS Mitigation Tools: Leveraging dedicated DDoS protection services and traffic scrubbing tools can aid in filtering out malicious traffic and ensuring that only legitimate requests reach the server.
- Regular Security Audits and Updates: Conducting frequent security audits and promptly applying necessary security updates and patches to web servers and applications can help in fortifying defenses against emerging vulnerabilities.
- Implementation of Rate Limiting and Filtering Rules: Employing rate limiting and filtering rules at the network perimeter or using dedicated firewall solutions can help mitigate the impact of Slowloris attacks by restricting the number of connections from individual IP addresses.

## Conclusion
The threat of Slowloris DDoS attacks serves as a stark reminder of the need for robust defense mechanisms and proactive security measures. Organizations and their security teams must understand the basics of Slowloris DDoS attacks, to better comprehend the sophisticated tactics employed by malicious actors. 

Understanding the intricacies of how a Slowloris attack operates is crucial in fortifying defenses against such stealthy and persistent threats. Organizations can use this knowledge to safeguard their digital assets and maintain operational continuity.

Ultimately, the trick to keeping such attacks off involves implementing robust security measures and continuously monitoring server activity to mitigate the risk of falling victim to Slowloris and similar DDoS attack techniques.