|
Date
May 1, 2001
Summary
A security vulnerability exists in Microsoft® IIS 5.0 on Windows
2000 which could potentially enable a malicious user to run code
of attacker’s choice in system context.
Summary from Securityfocus
Windows 2000 Internet printing ISAPI extension contains msw3prt.dll
which handles user requests. Due to an unchecked buffer in msw3prt.dll,
a maliciously crafted
HTTP .print request containing approx 420 bytes in the 'Host:' field
will allow the execution of arbitrary code. Typically a web server
would stop responding in a
buffer overflow condition; however, once Windows 2000 detects an
unresponsive web server it automatically performs a restart. Therefore,
the administrator will be unaware of this attack.
* If Web-based Printing has been configured in group policy, attempts
to disable or unmap the affected extension via Internet Services
Manager will be overridden by the group policy settings.
Issue
Windows 2000 introduced native support for the Internet Printing
Protocol (IPP), an industry-standard protocol for submitting and
controlling print jobs over HTTP. The protocol is implemented in
Windows 2000 via an ISAPI extension that is installed by default
on all Windows 2000 servers but which can only be accessed via IIS
5.0.
A security vulnerability results because the ISAPI extension contains
an unchecked buffer in a section of code that handles input parameters.
This could enable a remote attacker to conduct a buffer overrun
attack and cause code of her choice to run on the server. Such code
would run in the Local System security context. This would give
the attacker complete control of the server, and would enable her
to take virtually any action she chose.
The attacker could exploit the vulnerability against any server
with which she could conduct a web session. No other services would
need to be available, and only port 80 (HTTP) or 443 (HTTPS) would
need to be open. Clearly, this is a very serious vulnerability,
and Microsoft strongly recommends that all IIS 5.0 administrators
install the patch immediately. Alternatively, customers who cannot
install the patch can protect their systems by removing the mapping
for Internet Printing ISAPI extension.
Mitigating factors:
Servers on which the mapping for the Internet Printing ISAPI extension
has been removed are not at risk from this vulnerability. The process
for removing the mapping is discussed in the IIS 5.0 Security Checklist.
The High Security template provided in the checklist removes the
mapping, as does the Windows 2000 Internet Security Tool unless
the user explicitly chose to retain Internet Printing.
The attacker’s ability to extend her control from a compromised
web server to other machines would be heavily dependent on the specific
configuration of the network. Best practices recommend that the
network architecture reflect the position of special risk occupied
by network-edge machines like web servers and use measures like
DMZs and limited domain memberships to isolate such machines from
the rest of the network. Taking such measures would impede an attacker’s
ability to broaden the scope of the compromise.
Affected Products
Windows 2000 Server and Advanced Server
|