Unchecked Buffer in ISAPI Extension Could Enable Compromise of IIS 5.0 Server New

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.

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

Download

Patch: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=29321

Further Details

Source: Microsoft Corporat

Updated: May 1, 2001

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