PR07-40: Authentication Bypass, Passwords Leakage and SNMP Injection on
3Com AP 8760

Vulnerability Found: 6th November 2007

Vendor Informed: 2nd May 2008

Date Public: 14th November 2008

Severity: Medium

Credits: Adrian Pastor of ProCheckUp Ltd (www.procheckup.com). 

Vulnerability #1:

Description:

The HTTP authentication mechanism of the 3Com AP 8760 works as follows:

1. Router checks if credentials submitted by user are valid

2. If valid, the router's web interface redirects the user to URLs that
should only be available to authenticated admin users

What's important to note is that every time an "authenticated" URL is
accessed, there is _no_ authentication data being sent within HTTP
requests whatsoever. There are no passwords, or session IDs being
submitted at all within HTTP requests. Instead, the AP uses the
administrator's source IP address as authentication data.

This means that the authentication state relies on the false assumption
that post-authentication URLs won't be known by an attacker and that the
attacker and the administrator will _not_ share the same source IP
address. By simply accessing administrative URLs in a browser from _the
same IP address_ (i.e.: by sharing the same proxy or NATed IP address),
the authentication check can be bypassed completely.

Notes:

Although URL paths are different, these issues appear to be similar to
those found on other 3com router models:

http://www.securityfocus.com/bid/11408/discuss 
http://seclists.org/vulnwatch/2005/q1/0042.html 


Proof of concept:

The following is an example of an administrative page that would allow
an attacker to change settings:

http:///advanced.htm 


Vulnerability #2:

Description:

Additionally, sensitive data such as the admin password is returned
within certain pages. Although after bypassing the authentication the
attacker wouldn't need to know the admin password anyway, this could be
handy for a cracker in scenarios such as the following:

1. The authentication bypass is fixed by updating the firmware to a
patched version (attacker would still be able to access the device since
he/she knows the admin password)

2. The attacker could try the same password on other servers owned by
the same target company since it's a common human weakness to reuse
passwords.

Proof of concept:

The following URLs return the admin password within 'hidden' form fields:

http:///s_brief.htm 
http:///s.htm 


Vulnerability #3:

Description:

It's possible to launch SNMP injection attacks. By changing the system
name via SNMP, it's possible to inject a persistent XSS payload on
several pages including the _login page_. Thus, the attacker has an
opportunity to redirect the admin password to his own site by
overwriting the login form's action attribute.

The payload gets returned within the login page's 'title' tag. i.e.:



Example of snmpset command that changes the AP's system name:

snmpset -v2c -c private 192.168.1.1 sysName.0 s "PAYLOAD_GOES_HERE"


Successfully tested on:

3COM: AP8760: Dual Radio 11a/b/g Access Point, Software v2.1.13b05_sh,
Bootrom v1.2.1, Hardware R02

Note: model and firmware info extracted via SNMP from
'SNMPv2-MIB::sysDescr.0' OID.

Consequences:

Administrative access can be gained to the device without knowledge of
the admin password. The caveat is that the attacker must share the same
source IP address with the administrator. Therefore, this vulnerability
would mostly be exploited by internal users only. Sensitive information
such as administrative credentials can be obtained.

Admin passwords can be compromised given that an attacker has first
gained SNMP write access.


Workaround:

No workaround is available for the authentication bypass and passwords
leakage issue. SNMP injection can be resolved by disabling SNMP write
access.


References:

http://www.procheckup.com/ 
http://www.3com.com/products/en_US/detail.jsp?pathtype=purchase&tab=features&sku=3CRWE876075 


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