Linksys WRT54G Management Interface DoS Vulnerability iDEFENSE Security Advisory 09.13.05 www.idefense.com/application/poi/display?id=308&type=vulnerabilities September 13, 2005 I. BACKGROUND The Linksys WRT54G is a combination wireless access point, switch and router. More information is available at the following URL: http://www.linksys.com/products/product.asp?prid=508 II. DESCRIPTION Remote exploitation of an input validation error within the web management httpd component of Cisco Systems Inc.'s Linksys WRT54G wireless router may allow unauthenticated users to cause a denial of service (DoS). The vulnerability exists in several of the "POST" method handlers of the httpd running on the router's internal interfaces, including by default the wireless interface. In addition to not checking if authentication has failed until after data supplied by an external user has been processed, there are several places where the Content-Length is assumed to be valid. In some of those cases, data is read in without error checking while decrementing the length value. If the Content Length is set to a negative number, these checks will take an extremely long time, during which the httpd will become unresponsive. III. ANALYSIS An unauthenticated remote attacker may cause a DoS on the affected router. Exploitation of this vulnerability would require that an attacker can connect to the web management port of the router. The httpd is running by default, but is only accessible via the LAN ports or the WLAN (wireless LAN). Although this DoS is against the httpd itself, it may cause a higher than normal load on the router, which may be sufficient to cause packet loss. The httpd will also be unavailable. This may be sufficient to cause to owner to restart the device, which could in turn trigger changes made by a previous vulnerability. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in version 3.01.3 of the firmware of the Linksys WRT54G wireless router, and has identified the same code is present in versions 3.03.6 and 4.00.7. All versions prior to 4.20.7 may be affected. V. WORKAROUND To mitigate exposure of the internal network to outside attackers, ensure encryption is enabled on the wireless interface. The exact settings to use depend on your wireless deployment policies. VI. VENDOR RESPONSE http://www.linksys.com/servlet/Satellite?childpagename=US%2FLayout &packedargs=c%3DL_Download_C2%26cid%3D1115417109974%26sku%3D112491680264 5 &pagename=Linksys%2FCommon%2FVisitorWrapper VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet. VIII. DISCLOSURE TIMELINE 07/05/2005 Initial vendor notification 07/25/2005 Initial vendor response 09/13/2005 Coordinated public disclosure IX. CREDIT This vulnerability was discovered by Greg MacManus of iDEFENSE Labs. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.idefense.com X. LEGAL NOTICES Copyright (c) 2005 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@private for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.
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