Re: Cisco VPN Client can be used to gain local administrator rights (All Versions, patched or otherwise)

From: Sharad Ahlawat (sahlawat_at_CISCO.COM)
Date: 05/23/03

  • Next message: Russ: "Alert: Microsoft Security Bulletin - MS03-018" 
    Date:         Thu, 22 May 2003 19:30:37 -0700
To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM

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    This is in response to the mail sent by Nick Staff. The original mail is
    available at
    http://www.ntbugtraq.com/default.asp?pid=36&sid=1&A2=ind0305&L=ntbugtraq&F=P&S=&P=6219

    Physical access to the workstation and a valid user account are required to
    exploit this vulnerability which results in a person gaining local system
    administrative privileges. This vulnerability does not compromise the
    confidentiality of the data traversing the VPN tunnel established by the
    Cisco VPN Client.

    Upon initial confirmation of the vulnerability, Cisco bug CSCeb12179 was
    opened to address the issue. Cisco continues to work on its resolution with
    due urgency and will announce an updated version to its customers as soon as
    one is tested and available.

    The current workaround/mitigation technique is to make all the Cisco VPN
    client executable files read only for non administrative user groups.

    Cisco confirmed the report of this new vulnerability on May 15, 2003 and had
    requested joint disclosure with the reporter once a fix was tested and
    available for our customers.

    Cisco will continue to follow the guidelines of responsible disclosure with
    any reported vulnerabilities in its products. We welcome your reports and
    comments at psirt@cisco.com. For further information, please visit our web
    site at http://www.cisco.com/go/psirt .

    /Sharad

    On Thursday 22 May 2003 11:54, Nick Staff wrote:
    NS>First, before getting into this exploit I think it's only fair to say
    NS>that my last post, "Cisco Systems VPN Client allows local logon with
    NS>Elevated Privileges" was as Cisco's representative Sharad Ahlawat said,
    NS>outdated and already addressed (see following link):
    NS>
    NS>http://www.cisco.com/warp/public/707/vpnclient-multiple2-vuln-pub.shtml
    NS>
    NS>That said, I was sufficiently enough embarrassed to see if I could get
    NS>around their patched client, and here's how to do it:
    NS>
    NS>- Log on as a standard user.
    NS>- Browse to the C:\winnt directory, right click on explorer.exe and
    NS>choose copy.
    NS>- Browse to C:\Program Files\Cisco Systems\VPN Client (the directory
    NS>with ipsecdialer.exe) and paste a copy of explorer.exe into the folder.
    NS>- Double click on ipsecdialer.exe and select options > Windows logon
    NS>properties.
    NS>- Click on the first box to "enable start before log on".
    NS>- Click OK and Close.
    NS>- Rename ipsecdialer.exe to ipsecdialer.ex_
    NS>- Rename the copy of explorer.exe to ipsecdialer.exe
    NS>- Close any open windows.
    NS>- log out.
    NS>- log back on as the same standard user.
    NS>- Click okay on any error messages that appear.
    NS>- DO NOT CLOSE THE EXPLORER WINDOW THAT IS OPEN.
    NS>- At this point you may see your desktop or you may not (have had it
    NS>happen both ways), but whatever the case, that Explorer window is open
    NS>as local system and anything else you see is opened as the standard
    NS>user.
    NS>- In the open explorer window press the Up folder icon until you get to
    NS>My computer.
    NS>- Double click on Control Panel, then Administrative Tools, then
    NS>Computer Management
    NS>- Expand Local Users and Groups and add your Standard User account to
    NS>the Local Administrators Group.
    NS>
    NS>The following steps are provided to return your machine to it's previous
    NS>state (i.e. logging in without the client launching explorer)
    NS>
    NS>- Navigate to C:\Program Files\Cisco Systems\VPN Client and open the
    NS>vpnclient.ini file
    NS>- set runatlogon=0
    NS>- Save the file and restart the machine (Ctrl-Alt-Del if no Start
    NS>button)
    NS>
    NS>
    NS>And to Verify the Changes took...
    NS>
    NS>Log on as the Standard user and do whatever you want.
    NS>
    NS>Cisco has been notified about this issue and has acknowledged it, but
    NS>since asking for a week to test it further I have not heard from them
    NS>again.
    NS>
    NS>Possible Issue/Workaround
    NS>
    NS>I can't code, but it would seem the file at fault is csgina.dll which is
    NS>Cisco's replacement Gina that's installed automatically (and I assume is
    NS>what allows the explorer window to be launched in the system process).
    NS>Also, this exploit would be harder if not impossible were Cisco to
    NS>secure their install folder, but unfortunately even if I have
    NS>permissions set on the Program Files folder to only allow Users Read
    NS>access the Cisco install creates a subfolder which grants the
    NS>Interactive user Modify permissions. I think they do this because the
    NS>program constantly re-encrypts the group authentication key which is
    NS>stored in a text file in that directory.
    NS>
    NS>This has been Verified on Windows 2000 with SP3 and Windows 2003 Server
    NS>with the newest version of the Cisco VPN client (as well as older
    NS>versions too).
    NS>
    NS>Thanks,
    NS>
    NS>Nick Staff
    NS>
    NS>

    - --
    Sharad Ahlawat
    Cisco Product Security Incident Response Team (PSIRT)
    http://www.cisco.com/go/psirt
    Phone:+1 (408) 527-6087
    PGP-key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xC12A996C
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