ASUS Router Authentication Bypass / Cross Site Scripting

`ASUS router drive-by code execution via XSS and authentication bypass  
=====================================================================  
The latest version of this advisory is available at:  
https://sintonen.fi/advisories/asus-router-auth-bypass.txt  
  
  
Overview  
--------  
  
Various ASUS routers contain reflected Cross-Site Scripting (CWE-79) and   
authentication bypass (CWE-592) vulnerabilities that can be exploited to   
gain remote administrative access to the devices.  
  
  
Description  
-----------  
  
Several ASUS routers include reflected Cross-Site Scripting (CWE-79) and   
authentication bypass (CWE-592) vulnerabilities. An attacker who can lure   
a victim to browse to a web site containing a specially crafted JavaScript   
payload can execute arbitrary commands on the router as administrator   
(root). No user interaction is required.  
  
  
Impact  
------  
  
An attacker can create a JavaScript payload that uses an exploit to unearth  
the administrative password from the victim's ASUS router and logs in to   
the device. Once logged in the payload can perform administrative actions,   
including arbitrary command execution as administrator (root).  
  
  
Details  
-------  
  
The CSRF vulnerability CVE-2013-3093 discovered by Jacob Holcomb /   
Independent Security Evaluators (*) affecting various ASUS routers has been   
known for some time. The vulnerability enables an attacker to forge HTML   
forms and execute actions on the behalf of the target user (admin),   
enabling executing administrative functions. Another vulnerability allows   
executing arbitrary commands as administrator (root). ASUS was notified of   
these issues on March 29th 2013.  
  
These vulnerabilities were not considered critical, likely because of the   
seemingly strict prerequisites for the attack:  
  
"- The victim must have an active web application session on their ASUS  
router.  
- The victim must follow a link crafted by an attacker (e.g., by clicking   
the link directly, or through some other mechanism such as redirection   
from a malicious site).  
- The victim must have the necessary permissions to render and execute   
the forged HTTP."  
(*) http://securityevaluators.com/knowledge/case_studies/routers/Vulnerability_Catalog.pdf  
  
The two newly discovered vulnerabilities, described in more detail below,   
enable exploiting the earlier vulnerabilities in an automated fashion. The   
attack requires no interaction from the user, other than browsing to a   
website that has been injected with JavaScript code crafted by the attacker.   
The exploit could be embedded into various otherwise benign sites via e.g.   
malicious advertisement banners or by exploiting persistent Cross-Site   
Scripting vulnerabilities. The attacks could also be carried out with   
phishing email campaigns.  
  
The attack utilizes a reflected Cross-Site Scripting vulnerability on the   
unauthenticated error page to bypass the same-origin policy protection.   
Vulnerability number two described below is used to obtain the   
administrator's password. The reflected JavaScript payload executes within   
the context of the ASUS device and is able to utilize the CVE-2013-3093   
CSRF vulnerability to perform actions on the behalf of the user (admin).   
The exploit utilizes the "SystemCmd" arbitrary command execution feature   
to allow remote administrative telnet connectivity from all addresses.  
  
  
New vulnerabilities  
-------------------  
  
1. Reflected Cross-Site Scripting (CWE-79)  
  
There is a Cross-Site Scripting vulnerability on the router error page:  
  
http://192.168.1.1/error_page.htm?flag=%27%2balert(%27XSS%27)%2b%27  
  
The error page is accessible without authentication. This vulnerability   
enables the attacker to bypass same-origin policy restrictions enforced   
by XMLHttpRequest.  
  
  
2. Authentication bypass (CWE-592)  
  
The router error page http://192.168.1.1/error_page.htm includes the   
current administrative password in clear text.  
  
For example if the administrative password is "Joshua", the page includes   
the following dynamically generated JavaScript:  
  
if('1' == '0' || 'Joshua' == 'admin')  
  
The error page is accessible without authentication. This vulnerability   
enables the attacker with same-origin rights, obtained by utilizing the   
vulnerability above, to read the password by utilizing an XMLHttpRequest   
call. The script can then perform actions as administrator by utilizing   
further XMLHttpRequest calls.  
  
  
Vulnerable devices  
------------------  
  
The vulnerabilities were discovered from an ASUS RT-N16 device, firmware   
version 3.0.0.4.374_979. By sampling a small set of ASUS firmware images   
the following models were also found likely to be vulnerable:  
  
ASUS RT-N10U, firmware 3.0.0.4.374_168  
ASUS RT-N56U, firmware 3.0.0.4.374_979  
ASUS DSL-N55U, firmware 3.0.0.4.374_1397 *  
ASUS RT-AC66U, firmware 3.0.0.4.374_2050 *  
ASUS RT-N15U, firmware 3.0.0.4.374_16  
ASUS RT-N53, firmware 3.0.0.4.374_311  
  
*) ASUS DSL-N55U and ASUS RT-AC66U did not appear vulnerable to the   
authentication bypass issue. These devices are still vulnerable to the XSS   
and if the default password 'admin' has not been changed, they are easily   
exploitable as well.  
  
This list is by no means comprehensive. It is likely that other devices are   
vulnerable as well.  
  
  
Vendor recommendations  
----------------------  
  
1. Fix the Cross-Site Scripting vulnerabilities, at least from the   
unauthenticated part of the web interface (error_page.htm)  
2. Fix the admin password disclosure on error_page.htm  
3. Fix the CSRF (CVE-2013-3093) issue by utilizing anti-CSRF protection  
  
  
End user mitigation  
-------------------  
  
1. Install the latest firmware update, version 3.0.0.4.374.4422 or later.  
  
or  
  
2. If no firmware update has been released, the end users can partially   
mitigate the vulnerabilities by changing the "Router Login Name" via  
the "Administration - System" menu to be something other than "admin".   
Changing the router default network to something else than   
192.168.1.0/24 might also grant some limited protection.  
  
  
Proof-of-concept  
----------------  
  
A proof-of-concept exploit consisting of a small demo web page will be   
released at a later date.  
  
  
Credits  
-------  
  
The vulnerabilities were discovered by Harry Sintonen / nSense Oy.  
  
  
Previous work  
-------------  
  
The Cross-Site Request Forgery and command execution vulnerabilities  
(CVE-2013-3093) were discovered by Jacob Holcomb / Independent Security   
Evaluators.  
  
  
Timeline  
--------  
  
15.1.2014 discovered the vulnerabilities  
16.1.2014 wrote a preliminary report and PoC  
20.1.2014 attempted to send email to [email protected] and [email protected],   
both addresses bounced.  
20.1.2014 opened a ticket at vip.asus.com on how to report security  
vulnerabilities on ASUS hw.  
20.1.2014 emailed [email protected] asking how to report security  
vulnerabilities on ASUS hw.  
20.1.2014 emailed CERT-FI asking for help contacting ASUS.  
21.1.2014 CERT-FI was able to figure out ASUS security contact details.  
21.1.2014 reported the security vulnerabilities to ASUS.  
21.1.2014 reported the security vulnerabilities to CERT-FI vulncoord.  
22.1.2014 got a response from representative of the vendor, report forwarded to   
R&D for review. (ASUS CASEID=RPTM20140121202264-976)  
27.1.2014 got a response from the vendor, CWE-592 is fixed in the latest firmware  
version (for some devices?), CWE-79 is still being fixed.  
08.2.2014 the vendor reported that the updated firmware will be released   
during week 8.  
13.2.2014 ASUS released firmware updates for RT-N16, RT-N10U, RT-AC66U and   
RT-N15U.  
13.2.2014 requested CVE IDs from MITRE.  
19.2.2014 ASUS released a firmware update for RT-N56U.  
21.2.2014 released the security advisory.  
`