What is the Slowloris Attack?
The Slowloris attack is a specific kind of Denial-of-Service (DoS) attack that targets web servers to disrupt their usual work and make them inaccessible to legitimate users.
The term Slowloris is a reference to a slow-moving animal that carries out this particular attack by exploiting the fundamental restriction inherent in the way the HTTP connections are handled by web servers.
Sharp contrast was marked when Slowloris was initially introduced as a different kind of Dos technique that was not common then, but rather, it involved flooding the target server with a large number of requests.
On the other hand, Slowloris was designed to take advantage of problems related to the web server software’s performance in managing concurrent connections.
These attacks differed from traditional DoS attacks that launched a high-traffic flood at the server. However, Slowloris attacks are more stealthy, they use the servers simultaneous requests processing mechanism to attack it.
It utilizes the technique of developing multiple connections to the server target but sending HTTP headers extremely slowly. By slowing down the header transmission, the attacker may keep the suitable connections open for long intervals and utilize scarcely any bandwidth.
How does it Work?
To understand how Slowloris works, let’s delve into the typical lifecycle of an HTTP connection:
- Connection Establishment: A slowloris attack is carried out in a way that invokes multiple simultaneous connections to the target web server. These connections can be the result of a single attacked machine or the entire system that can accommodate many computers, which depends on the level of the attack.
- Server Processing: Once he gets the request, the server processes the details and answers back with the requested content (e.g., web page, image, or file).
- Connection Closure: Thereafter, the server sends the response, the client’s connection is closed, and the content they require is retrieved.
Slowloris disrupts this process by starting plenty of connections to the target server at the time when only HTTP headers are sent at a slow pace. The intruder does not send out complete requests now, he sends part of the HTTP headers in small bits so that they remain open as long as possible with each connection.
This following effect can be explained through pinning down the activities of those resources like thread pools, memory and network connections. As the server absorbs the demand of its limited supply gradually, it will come to a point where it cannot even bear requests from authentic users.
Consequently, the end-users of the targeted website have either total loss of service or experience slow response time which denotes any legitimate visitor.
As such, Slowloris mechanics are focused on overloading the server, the way it consumes incoming connections and constantly bombarding it with partial HTTP requests. As these connections take too long to establish, the server consumes the exiguous resources for legitimate users.
Signs to Identify the Slowloris Attack
Distinguishing a Slowloris attack should be recognized as one of the important measures that need to be taken quickly to reduce its negative effects on the availability and performance of a web server.
Slowloris Attacks are being executed with stealth and deception hence these cannot be detected easily by the normal security procedures.
Nonetheless, some distinctive features and indicators can always help web servers to detect the presence of Slowloris attack. Let’s explore these signs in detail:
1. Gradual Degradation in Performance
With any continuing Slowloris assault, there is a clear decrease in the performance of the affected web server among the key indicators of a Slowloris attack. In the initial phase, the server may be able to respond to the requests for legitimate users at a normal speed.
In the beginning, this is hardly perceivable but as the attack continues and the number of open connections rises; the server’s speed drops and eventually becomes sluggish.
Users can experience problems with the web pages’ loading (lags or frequency of the same), slow page load times, and timeouts while trying to interact with the server software.
2. Abnormal Traffic Patterns
Consequently, Slowloris DDoS (Distributed Denial of Service) Attacks tend to use traffic signals that are different from those usually encountered during active user activity.
The network flow may be monitored by using special tools or intrusion detection systems(IDS), and the unusual activities that look like the SlowLoris attack will be detected.
This could be demonstrated through the growing number of established connections to the main server, the increased duration of such connections, or a higher number of long-term requests with delayed transmission velocity.
3. Long-Duration Connections
In the case of usual HTTP links, which time is only short and transient, links last for a pretty long time. Slowloris’s approach here is through partial HTTP requests that are sent at a dangerously slow speed, which eventually prevents easy server overloading and hence leaves it exposed to several attacks.
Specific tools might reveal the fact that there is expanded connectivity whose duration is too long, which usually reflects minimal traffic transmission.
4. Server Error Responses
The nature of Slowloris’s attack is such that it leads to the server’s resources being overstressed. This, consequently, causes a wave of error responses to come back to the requests sent by legitimate users who try to access the site web.
Sometimes, the error responses are given as HTTP 503 Service Unavailable and HTTP 408 Request Timeout. Such reception messages suppose that the server does not have the ability to manage incoming requests because of a slow loris attack, which is, in turn, caused by server resource exhaustion.
5. Unusually High Resource Utilization
Their flow of requests in Nordicels assault shares resources, including CPU cycles, memory, and network bandwidth, just to keep vast quantities of connections open.
The monitoring task can be managed by administrators through systems monitoring tools or performance monitoring solutions which are able to record server utilization metrics.
A remarkably elevated level of resources, particularly if they are exploited during periods when user activity is low, may signal that the slowloris attack is in effect.
6. Suspicious Access Patterns in Logs
Seeing server access log is most likely to indicate the type of incoming requests and slowloris pattern of attack as well as can reveal suspicious access patterns.
Administrators may observe, inter alia, recurring partial HTTP requests, new connections occurring from a single or the same addresses, and those used for requests remaining inactive for longer. The Access Log records are analyzed in synchrony with other probability indicators to assist in striking a Slowloris attack.
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