ACO BadURLChars doesn't block /%2F from URL, request gets 404 from Apache instead of 500
Article ID: 6546
Updated On:
Products
Issue/Introduction
I'm protecting a Web Site with the Web Agent, and when the request has "/%2F", I see a strange behavior. The Web Agent
doesn't block the request. As result, the browser shows error 404 "Not Found", rather than expected 500 error
that should be returned by the Web Agent.
The Web Agent ACO badurlchars is configured with "/%2f,//,./,/.,/*,*.,~,\,%00-%1f,%7f-%ff,%25". With this configuration
the Web Agent should block the request. Why it doesn't ?
Environment
Cause
The reason we are getting 404 when %2f is because APACHE itself is breaking the URL.
In order to avoid it we need to add in Apache Configuration : "AllowEncodedSlashes" to ON.
Description: Determines whether encoded path separators in URLs are allowed to be passed through
Syntax: AllowEncodedSlashes On|Off|NoDecode
Default: AllowEncodedSlashes Off
Context: server config, virtual host
Status: Core
Module: core
Compatibility: Available in Apache httpd 2.0.46 and later. NoDecode option available in 2.2.18 and later.
The AllowEncodedSlashes directive allows URLs which contain encoded path separators (%2F for / and additionally %5C for \ on accordant systems) to be used in the path info.
With the default value, Off, such URLs are refused with a 404 (Not found) error.
With the value On, such URLs are accepted, and encoded slashes are decoded like all other encoded characters.
With the value NoDecode, such URLs are accepted, but encoded slashes are not decoded but left in their encoded state.
Turning AllowEncodedSlashes On is mostly useful when used in conjunction with PATH_INFO.
http://httpd.apache.org/docs/2.2/mod/core.html#allowencodedslashes
Resolution
Add in Apache Configuration: "AllowEncodedSlashes" to ON to solve the issue
Additional Information
Further reading about that specific Apache behavior : urlencoded Forward slash is breaking URL
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