Cisco IKE Implementation Group Name Enumeration

`Trustwave SpiderLabs Security Advisory TWSL2013-004:  
Group Name Enumeration Vulnerability in Cisco IKE Implementation  
  
https://www.trustwave.com/spiderlabs/advisories/TWSL2013-004.txt  
  
Published: 04/18/13  
Version: 1.0  
  
Vendor: Cisco (www.cisco.com)  
Product: ASA (Adaptive Security Appliance)  
Versions affected: 8.4(2), 8.4(5), 9.1(1)  
  
Product description:  
The Cisco ASA 5505 Adaptive Security Appliance is a next-generation,  
full-featured security appliance for small business, branch office, and  
enterprise teleworker environments. The Cisco ASA 5505 delivers  
high-performance firewall, SSL and IPsec VPN, and rich networking services  
in a modular, "plug-and-play" appliance.  
  
  
Finding 1: Group Name Enumeration  
**** Credit: Daniel Turner of Trustwave SpiderLabs  
CVE: CVE-2013-1194  
CWE: CWE-206  
  
Each VPN configuration is assigned a group name, which is used to manage  
separate Security Associations. Previous advisories have found that when a  
VPN endpoint is configured to allow Aggressive Mode IKE negotiations using  
PSK, a hash of the PSK can be captured and potentially cracked offline. In  
order to successfully crack this hash a correct group name is required.  
  
The above product versions are susceptible to a group name enumeration  
vulnerability, because of a difference in the way the device responds to  
correct and incorrect group names sent in the initial exchange packet.  
  
Similar to CSCeg00323 and CSCtj96108 where this was possible because of no  
response and a response with a DPD payload respectively. It has been found  
that it remains possible to distinguish a correct group name by the number  
of response packets sent by the device. A correct group name elicits three  
attempts to continue the handshake and an additional encrypted phase 2  
packet, while the device will only respond twice to an incorrect group.  
Enumeration is slow because of the requirement to wait for the responding  
packets, but this has been successfully accomplished. Below are examples of  
the different responses:  
  
Example 1:  
  
#Request using invalid group name  
  
ike-scan 10.70.70.25 -M -A --id=incorrectgroup  
  
#Response using invalid group name  
  
13:22:59.929273 IP 10.70.70.204.isakmp > 10.70.70.25.isakmp: isakmp: phase 1 I agg  
13:22:59.932624 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 1 R agg  
13:23:05.696571 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 1 R agg  
  
Example 2:  
  
#Request using valid group name  
  
ike-scan 10.70.70.25 -M -A --id=correctgroup  
  
#Response using valid group name  
  
13:23:05.693673 IP 10.70.70.204.isakmp > 10.70.70.25.isakmp: isakmp: phase 1 I agg  
13:23:13.690392 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 1 R agg  
13:23:21.690464 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 1 R agg  
13:23:29.690528 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 1 R agg  
13:23:37.691275 IP 10.70.70.25.isakmp > 10.70.70.204.isakmp: isakmp: phase 2/others R inf[E]  
  
This information can be used to capture and crack a weak PSK if Aggressive  
Mode is enabled.  
  
Remediation Steps:  
The vendor will be releasing security fixes to the above issues and affected  
versions can be patched by installing the 8.4(6) firmware or the 9.1(2)  
firmware for the Cisco ASA platform. Administrators with other affected  
firmware versions should be aware that this information could be  
potentially be revealed and it is recommended that factory default group or  
easily guessable group names are not used.  
  
Additional Credits:  
Jonathan Claudius of Trustwave SpiderLabs: Confirmation of  
Vulnerability/Behavior on Cisco ASA 8.4(5) and 9.1(1)  
  
Revision History:  
02/21/13 - Vulnerability disclosed  
03/14/13 - Vendor acknowledges security issue  
04/17/13 - Vendor releases security alert  
04/18/13 - Advisory published  
  
References  
1. http://www.cisco.com/warp/public/707/cisco-sn-20050624-vpn-grpname.shtml  
2. http://www.cisco.com/en/US/products/csr/cisco-sr-20101124-vpn-grpname.html  
3. http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2013-1194  
  
About Trustwave:  
Trustwave is the leading provider of on-demand and subscription-based  
information security and payment card industry compliance management  
solutions to businesses and government entities throughout the world. For  
organizations faced with today's challenging data security and compliance  
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solutions that include its flagship TrustKeeper compliance management  
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Australia. For more information, visit https://www.trustwave.com  
  
About Trustwave SpiderLabs:  
SpiderLabs(R) is the advanced security team at Trustwave focused on  
application security, incident response, penetration testing, physical  
security and security research. The team has performed over a thousand  
incident investigations, thousands of penetration tests and hundreds of  
application security tests globally. In addition, the SpiderLabs Research  
team provides intelligence through bleeding-edge research and proof of  
concept tool development to enhance Trustwave's products and services.  
https://www.trustwave.com/spiderlabs  
  
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