Slowloris Multiple HTTP Server Denial of Service Attack Tool
IntelliShield: Applied Mitigation Bulletin
2009 June 18 18:26 GMT
2016 July 22 14:57 GMT
Additional information is available regarding Snort signatures that can help detect and prevent attacks that use the Slowloris tool.
Slowloris, an attack tool that could allow an unauthenticated, remote attacker to exhaust available connections on targeted HTTP servers, has been publicly released.
The tool is designed to slowly send incomplete HTTP requests to an HTTP server. The format of the request could cause the server to continue to wait for input on an established connection. Sending the malicious HTTP requests requires little bandwidth on the behalf of the attacker, decreasing the network resources required for exploitation. By using the tool, an attacker could cause the targeted server to become unresponsive and unable to process further requests due to the exhaustion of allowed HTTP connections.
HTTP servers that are known to be affected include the Apache HTTP Server and the Squid HTTP Proxy. Microsoft IIS Servers version 6.0 and 7.0 are reportedly unaffected by the tool. Sites configured with load balancers may be at less risk of isolated attack because a single attack host could be unable to send enough requests to exhaust HTTP connections. Network filtering, including the use of intrusion prevention service (IPS) devices, may block malformed HTTP requests.
Administrators can apply Snort SID 21104 to help prevent attacks that attempt to exploit this vulnerability.
The security vulnerability applies to the following combinations of products.
Security Activity Bulletin
Original Release Base
The urgency and severity ratings of this alert are not tailored to individual users; users may value alerts differently based upon their network configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.