Title: Microsoft ISA Server Web Proxy DoS Vulnerability
Severity: HIGH
Description:
Microsoft Internet Security and Acceleration (ISA) Server is a configurable firewall and proxy server. ISA Server implements secure internet access and accelerates internet usage through caching. The Web Proxy service (W3PROXY.EXE)enables internal users to make requests for external web resources via the firewall. This ensures that internal user requests are fulfilled through secure transactions.
The Web Proxy service (W3PROXY.EXE) implemented in Microsoft ISA Server is subject to denial of service attacks. This issue arises from the way in which requests are handled by the Web Proxy service.
If a HTTP request with an unusually long path is submitted, the Web Proxy service could stop responding on the target host.
This vulnerability is only exploitable from the internal network unless the Web Publishing service has been enabled, in which case it can be exploited from either internal or external networks. It is disabled by default.
A HTML email containing the malicious URL in an image tag or a javascript URL, could invoke a user's browser. An attempt to fulfill this request by the Web Proxy service, could permit a denial of service condition on an internal users system. This is a potential way a remote attacker could exploit this vulnerability even if Web Publishing is disabled.
Successful exploitation of this vulnerability will only affect the Web Proxy service, disallowing inbound or outbound web traffic.
A restart of the service is required in order to gain normal functionality.
* It has been reported that the execution of arbitrary commands is possible. If this is the case the complete remote compromise of the host may be achievable. The latest findings have not been confirmed by anyone other than the person who posted about it.
Affected Products:
- Microsoft ISA Server 2000 0.0.0
- Microsoft Small Business Server 2000 0.0.0
- Microsoft Small Business Server 2003 Premium Edition 0.0.0
References:
- Microsoft: Microsoft Security Bulletin MS01-021
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