Slowloris – HTTP DoS Tool in PERL

Outsmart Malicious Hackers


This tool has been hitting the news, including some mentions in the SANS ISC Diary.

It’s not actually a new attack (it’s been around since 2005) but this is the first time a packaged tool has been released for the attack.

Slowloris holds connections open by sending partial HTTP requests. It continues to send subsequent headers at regular intervals to keep the sockets from closing. In this way webservers can be quickly tied up. In particular, servers that have threading will tend to be vulnerable, by virtue of the fact that they attempt to limit the amount of threading they’ll allow.

Slowloris must wait for all the sockets to become available before it’s successful at consuming them, so if it’s a high traffic website, it may take a while for the site to free up it’s sockets. So while you may be unable to see the website from your vantage point, others may still be able to see it until all sockets are freed by them and consumed by Slowloris. This is because other users of the system must finish their requests before the sockets become available for Slowloris to consume. If others re-initiate their connections in that brief time-period they’ll still be able to see the site.

So it’s a bit of a race condition, but one that Slowloris will eventually always win – and sooner than later.

Slowloris lets the webserver return to normal almost instantly (usually within 5 seconds or so). That makes it ideal for certain attacks that may just require a brief down-time.

This affects a number of webservers that use threaded processes and ironically attempt to limit that to prevent memory exhaustion – fixing one problem created another. This includes but is not necessarily limited to the following:

  • Apache 1.x
  • Apache 2.x
  • dhttpd
  • GoAhead WebServer
  • Squid

There are a number of webservers that this doesn’t affect as well, in the authors testing:

  • IIS6.0
  • IIS7.0
  • lighttpd
  • nginx
  • Cherokee (verified by user community)

You can download Slowloris here:

slowloris.pl

Or read more here.

Posted in: Exploits/Vulnerabilities, Networking Hacking, Web Hacking

, , , , ,


Latest Posts:


snallygaster - Scan For Secret Files On HTTP Servers snallygaster – Scan For Secret Files On HTTP Servers
snallygaster is a Python-based tool that can help you to scan for secret files on HTTP servers, files that are accessible that shouldn't be public and can pose a s
Portspoof - Spoof All Ports Open & Emulate Valid Services Portspoof – Spoof All Ports Open & Emulate Valid Services
The primary goal of the Portspoof program is to enhance your system security through a set of new camouflage techniques which spoof all ports open and also emulate valid services on every port.
Cambridge Analytica Facebook Data Scandal Cambridge Analytica Facebook Data Scandal
One of the biggest stories of the year so far has been the scandal surrounding Cambridge Analytica that came out after a Channel 4 expose that demonstrated the depths they are willing to go to profile voters, manipulate elections and much more.
GetAltName - Discover Sub-Domains From SSL Certificates GetAltName – Discover Sub-Domains From SSL Certificates
GetAltName it's a little script to discover sub-domains that can extract Subject Alt Names for SSL Certificates directly from HTTPS websites which can provide you with DNS names or virtual servers.
Memcrashed - Memcached DDoS Exploit Tool Memcrashed – Memcached DDoS Exploit Tool
Memcrashed is a Memcached DDoS exploit tool written in Python that allows you to send forged UDP packets to a list of Memcached servers obtained from Shodan.
QualysGuard - Vulnerability Management Tool QualysGuard – Vulnerability Management Tool
QualysGuard is a web-based vulnerability management tool provided by Qualys, Inc, which was the first company to deliver vulnerability management services as a SaaS-based web-service.


5 Responses to Slowloris – HTTP DoS Tool in PERL

  1. Greg June 23, 2009 at 10:06 am #

    As i saw it appearing on Milw0rm, i knew this will be a headliner :)

  2. Motoma June 23, 2009 at 6:08 pm #

    There is a python version of this titled PyLoris which runs in Windows, Linux, and Mac OS X.

  3. David June 23, 2009 at 6:12 pm #

    Another great sharing from RSnake. Tool very well developed and I already tested with success on my home pen-testing. Top of the news!

  4. droope June 24, 2009 at 2:41 am #

    uh, that seems like a fun tool.

    I can smell all fellow script kiddies enjoying this.

  5. Jeff Price June 24, 2009 at 6:38 pm #

    I wrote this version a few years ago in bash

    #!/bin/bash
    while true; do
    printf “GET / HTTP/1.0\n”|nc $1 80 &
    done