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:
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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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