1.4.4 Disallow non-ASCII Characters in URLs - Applications

Information

This feature is used to allow or reject all requests to IIS 7 that contain non-ASCII characters. When using this feature, Request Filtering will deny the request if high-bit characters are present in the URL. The UrlScan equivalent is AllowHighBitCharacters. It is recommended that requests containing non-ASCII characters be rejected, where possible.

This feature can help defend against canonicalization attacks, reducing the potential attack surface of servers, sites, and/or applications.

Solution

The AllowHighBitCharacters Request Filter may be set for a server, website, or application using the IIS Manager GUI, using AppCmd.exe commands in a command-line window, and/or directly editing the configuration files. To configure using the IIS Manager GUI:
1. Open Internet Information Services (IIS) Manager
2. In the Connections pane, go to the connection, site, application, or directory to be configured
3. In the Home pane, double-click Request Filtering
4. Click Edit Feature Settings... in the Actions pane
5. Under the General section, uncheck Allow high-bit characters

Note: Disallowing high-bit ASCII characters in the URL may negatively impact the functionality of sites requiring international language support.

See Also

https://benchmarks.cisecurity.org/tools2/iis/CIS_Microsoft_IIS_8_Benchmark_v1.4.0.pdf

Item Details

Category: SYSTEM AND INFORMATION INTEGRITY

References: 800-53|SI-10

Plugin: Windows

Control ID: bd735451447be4fb1e210af9a9b76ebeac4cf323431313dd09103745097b1d1c