The process can be further slowed if legitimate sessions are reinitiated. A Slowloris attack must wait for sockets to be released by legitimate requests before consuming them one by one.įor a high-volume web site, this can take some time. Named after a type of slow-moving Asian primate, Slowloris really does win the race by moving slowly and steadily. Ultimately, the targeted server’s maximum concurrent connection pool is filled, and additional (legitimate) connection attempts are denied.īy sending partial, as opposed to malformed, packets, Slowloris can easily slip by traditional Intrusion Detection systems. Periodically, the Slowloris sends subsequent HTTP headers for each request, but never actually completes the request. The attacked servers open more and connections open, waiting for each of the attack requests to be completed. It does this by continuously sending partial HTTP requests, none of which are ever completed. You can set it short because you also tell. You set it with a base ammount of time to wait before closing the connection. modreqtimeout doesnt care if a request ever gets complete, after so much time it will just time out. The target opens a thread for each incoming request, with the intent of closing the thread once the connection is completed. Slowloris opens a lot of connections and never completes the request, so the server sits there waiting for it to complete.
Slowloris works by opening multiple connections to the targeted web server and keeping them open as long as possible. A Slowloris attack occurs in 4 steps: The attacker first opens multiple connections to the targeted server by sending multiple partial HTTP request headers. Notably, it was used extensively by Iranian ‘hackivists’ following the 2009 Iranian presidential election to attack Iranian government web sites. Over the years, Slowloris has been credited with a number of high-profile server takedowns.
Slowloris has proven highly-effective against many popular types of web server software, including Apache 1.x and 2.x. Due the simple yet elegant nature of this attack, it requires minimal bandwidth to implement and affects the target server’s web server only, with almost no side effects on other services and ports.
QS_SrvMinDataRate - This setting requires a minimum of 150 bytes per second per connection, and limits the connection to 1200 bytes per second when the server reaches the MaxClients limit.Developed by Robert “ RSnake” Hansen, Slowloris is DDoS attack software that enables a single computer to take down a web server. Mitigate Slow HTTP GET/POST Vulnerabilities in the Apache HTTP Server Ian Muscat JA slow HTTP Denial of Service attack (DoS), otherwise referred to as the Slowloris HTTP attack, makes use of HTTP GET requests to occupy all available HTTP connections permitted by a web server.QS_SrvMaxConnClose - This setting disables the KeepAlive function when at least 180 connections exist.QS_SrvMaxConnPerIP - This setting limits each IP address to a maximum number of 50 connections.QS_ClientEntries - This setting tracks up to 100,000 connections.MaxClients - This setting limits the maximum number of connections to 256.This example configuration will enforce the following behavior: slowloris keeping connections open without requesting anything): QS_SrvMinDataRate 150 1200 # and limit request header and body ( careful, that limits uploads and post requests too): # LimitRequestFields 30 # QS_LimitRequestBody 102400 # handles connections from up to 100000 different IPs QS_ClientEntries 100000 # will allow only 50 connections per IP QS_SrvMaxConnPerIP 50 # maximum number of active TCP connections is limited to 256 MaxClients 256 # disables keep - alive when 70 % of the TCP connections are occupied: QS_SrvMaxConnClose 180 # minimum request / response speed ( deny slow clients blocking the server, ie.