Onderwerp: Nortel Networks Contivity VPN Client information leakage vulnerability

Name: User Account Enumeration in Nortel Contivity VPN
Vendor: Nortel Networks
Products Affected: Nortel Networks Contivity VPN Client
Type: Remote User Account Enumeration
Severity: Medium

I. Overview
The Nortel Networks Contivity VPN Client authentication error message
provides more information than is necessary, thus allowing an attacker
to discover existing users on the system. This bug was discovered as
part of a penetration test we carried out on the VPN server of a client.

II. Description
1. If a valid user name and an invalid password is given, the Contivity
VPN Client displays "Login Failure due to: authentication failure"
2. If an invalid user name is given, the Contivity VPN Client displays
"Login Failed: Please verify the entered login information is correct".

III. Impact
The different error messages could enable a malicious person to guess
valid user names on the Contivity VPN/Firewall, and then launch
password-guessing attacks against these accounts.

IV. Solution
This issue is resolved in Contivity VPN Client for Windows V5.01_030

Refer to the CERT VU Note at
http://www.kb.cert.org/vuls/id/830214 and our full advisory at
http://www.nii.co.in/vuln/contivity.html
for information about vendor response, applying the patches, and other
technical details.

V. About Network Intelligence India
We're a leading provider of information security services and products.
Our AuditPro suite of security assessment software provides
comprehensive, policy-based security audits for Windows 2000, 2003, XP,
Redhat Linux, Sun Solaris, Oracle and MS SQL Servers. For more
information, visit us at http://www.nii.co.in

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> IV. Solution
> This issue is resolved in Contivity VPN Client for
Windows V5.01_030

Obviously this can't be fixed by changing the client
software. The full advisory makes it clear that an
attacker willing to reverse engineer the proprietary
hash used to obscure usernames in Nortel's software
could still exploit this vulnerability.

Interestingly, the advisory claims that the leakage is
inherent in the aggressive IKE protocol. Does that
mean all other VPN servers using aggressive IKE leak
too?




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