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NULL Sessions Vulnerabilities Using Alternate Named Pipes
------------------------------------------------------------------------
SUMMARY
By taking advantage of hardcoded named pipes allowed for NULL sessions and
using the property of MSRPC that, by default, all available RPC interfaces
in a process can be reached using any opened endpoint, it is possible to
anonymously enumerate Windows services and read the Application and System
eventlogs.
DETAILS
Vulnerable Systems:
* Windows NT 4.0, Windows 2000 prior to URP1 for Windows 2000 SP4
Windows XP and Windows Server 2003 are not directly affected by the
vulnerabilities described in this document.
Still, the alternate named pipes technique also applies to Windows XP and
Windows Server 2003, including Windows XP SP2 and Windows Server 2003 SP1.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2150>
CAN-2005-2150
Anonymous Windows service enumeration:
The svcctl MSRPC interface is used to communicate with the
<http://www.hsc.fr/ressources/articles/win_net_srv/ch04s07s09.html>
Windows SCM (Service Control Manager).
The svcctl vulnerability allows an anonymous user to connect to the SCM
(Service Control Manager). It is then possible to enumerate installed or
running services. See image at:
<http://www.hsc.fr/ressources/presentations/null_sessions/img16.html>
http://www.hsc.fr/ressources/presentations/null_sessions/img16.html
Depending on the security descriptor protecting each service (stored in
binary under the Security registry subkey of each service's subkey), it
might be possible to anonymously start or even stop a Windows service.
Because in Windows NT 4.0 and Windows 2000, the EVERYONE group contains
the ANONYMOUS LOGON SID, a service with a weak DACL allowing members of
the EVERYONE group to start (or stop) the service can be remotely started
or stopped anonymously.
For more information about services permissions, see
<http://cert.uni-stuttgart.de/archive/bugtraq/2004/10/msg00159.html>
http://cert.uni-stuttgart.de/archive/bugtraq/2004/10/msg00159.html
Anonymousl Application and System eventlogs read:
The <http://www.hsc.fr/ressources/articles/win_net_srv/ch04s07s06.html>
eventlog MSRPC interface is used to communicate with the Windows eventlog
service. The eventlog vulnerability can be used to anonymously read either
the Application or System eventlog of a remote Windows NT 4.0 or Windows
2000 system.
It is not possible to read the Security eventlog because a specific
Windows privilege must be held by the caller process
(SeSecurityPrivilege).
Vendor Status:
Both vulnerabilities are fixed in the URP1 for Windows 2000 SP4 recently
released by the vendor: <http://support.microsoft.com/kb/900345/>
http://support.microsoft.com/kb/900345/
The svcctl vulnerability was fixed by modifying the SCM DACL (enforced
when the OpenSCManager{A,W} operation is used), denying access for the
ANONYMOUS LOGON SID.
The eventlog vulnerability was fixed by using a RPC callback function for
the eventlog interface, to reject unauthenticated binds.
Workarounds:
It is possible to protect against the eventlog vulnerability by adding and
setting to 1 the RestrictGuestAccess registry value, under the following
two registry keys:
HKLM\SYSTEM\CurrentControlSet\Services\Eventlog\Application\
HKLM\SYSTEM\CurrentControlSet\Services\Eventlog\System\
In Windows 2000, the RestrictGuestAccess value can be set using the
following security options:
* Restrict guest access to application log
* Restrict guest access to system log
These settings are mentioned in the following article:
<http://support.microsoft.com/kb/842209>
http://support.microsoft.com/kb/842209
It is recommended to set these registry values on Windows NT 4.0 systems,
where no other workaround is available.
Vulnerability Assessment:
svcctl vulnerability:
<http://www.nessus.org/plugins/index.php?view=single&id=18585>
http://www.nessus.org/plugins/index.php?view=single&id=18585
eventlog vulnerability:
<http://www.nessus.org/plugins/index.php?view=single&id=18602>
http://www.nessus.org/plugins/index.php?view=single&id=18602
For more information, see the following documents:
* <http://www.hsc.fr/ressources/presentations/null_sessions/> MSRPC null
sessions: exploitation and protection
* <http://www.hsc.fr/ressources/articles/win_net_srv/> Windows network
services internals
Disclosure Timeline:
2004/01/23: Vulnerability reported to vendor
2004/02/12: Vendor announces its intention to release fixes as part of the
next Windows 2000 Service Pack
2004/09/09: A related vulnerability affecting Windows XP SP2 is published
2005/02/08: Release of MS05-007, fixing a specific instance of a similar
vulnerability in Windows XP and Windows XP SP2
2005/02/28: Private versions of Windows 2000 fixes available for test
2005/03/30: Confirmation that tested fixes correct the vulnerability
2005/06/28: Release of URP1 for Windows 2000 SP4, which includes fixes for
Windows 2000
ADDITIONAL INFORMATION
The information has been provided by
<mailto:Jean-Baptiste.Marchand@hsc.fr> Jean-Baptiste Marchand.
The original article can be found at:
<http://www.hsc.fr/ressources/presentations/null_sessions/>
http://www.hsc.fr/ressources/presentations/null_sessions/
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