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Re: Potential HTTP Header Injection in Apache HTTPClient
From: David Jorm <djorm () redhat com>
Date: Fri, 15 Feb 2013 13:08:07 +1000

On 02/13/2013 07:54 PM, Kurt Seifried wrote:
Hash: SHA1

On 01/10/2013 07:38 AM, chevalier 3as wrote:

As I'm not sure if this is a vulnerability or simply a 'feature',
I'm posting the details for more information.

The addRequestHeader method of the Apache HTTPClient module
version 3.x seems to allow the injection of more than a header
(potentilally the latest version 4.x too for addHeader method):

Using the following code, it includes a third header in the
request: HttpClient client = new HttpClient(); PostMethod method =
new PostMethod("http://www.google.fr";);
method.addRequestHeader("header1", "value1\r\nheader3: value3");

The real risk is adding a second request using a similar code:
req.addRequestHeader("Content-Length:0\r\n\r\n" +
"POST\t/anotherpath\tHTTP/1.1\r\n" + "Host:host\r\n" +
"Referer:faked\r\n" + "User-Agent:faked\r\n" +
"Content-Type:faked\r\n" + "Content-Length:3\r\n" + "\r\n" +
"foo\n", "bar");

Because of the Content-Length header, the sever will consider it as
a seperate request.

Iis this an expected behavior ? if so developpers should be aware
of the risk letting a user input values.

A similar advisory for Flash is available here:

My 2 cents, As

Has anyone investigated this/can comment on this? thanks.

I do not think this qualifies as a vulnerability. The addRequestHeader method isn't stripping out CRLF, allowing for a potential header splitting attack if an application passes unsanitized user input to addRequestHeader. The onus should be on the application to sanitize user input appropriately. If we called this a vulnerability, then we'd have to say a database interface that lets you pass an SQL string might allow for SQL injection, or something that lets you print a string to the body of a HTTP response might allow for XSS.

Having an optional parameter to addRequestHeader to sanitize CRLF values might be a nice feature, but I'd call it a feature request rather than a vulnerability.


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