HTTP Tolerant Request Parsing

Products

• ProxySG Software - SGOS

Issue/Introduction

 

Understanding Tolerant HTTP Request Parsing By default, the ProxySG blocks malformed HTTP requests, returning a 400 Invalid Request error. The tolerant HTTP request parsing flag causes certain types of malformed requests to be processed instead of being rejected.

 

By default, a header line not beginning with a <Tab> or space character must consist of a header name (which contains no <Tab> or space characters), followed by a colon, followed by an optional value, or an error is reported. With tolerant request parsing enabled, a request header name is allowed to contain <Tab> or space characters, and if the request header line does not contain a colon, then the entire line is taken as the header name.

A header containing one or more <Tab> or space characters, and nothing else, is considered ambiguous. Blue Coat does not know if this is a blank continuation line or if it is the blank line that signals the end of the header section. By default, an ambiguous blank line is illegal, and an error is reported. With tolerant request parsing enabled, an ambiguous blank line is treated as the blank line that signals the end of the header section.

 

 

Resolution

To Enable the HTTP Tolerant Request Parsing Flag through the CLI

 

Note: This feature is only available through the CLI. It cannot be set through the Management Console. Also this is global command (you can not apply this for individual URL/Domain).

 

From the (config) prompt, enter the following command to enable tolerant HTTP request parsing (the default is disabled):

SGOS#(config) http tolerant-request-parsing

 

To disable HTTP tolerant request parsing, enter the following command:

SGOS#(config) http no tolerant-request-parsing

 

Here is the GET requests from working and non-working.

400 Bad Request:

GET http://www.google.com/trends?q=annka+sorenstam,+michelle+wie HTTP/1.0

Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-silverlight, application/x-silverlight-2-b2, */*

Accept-Language: en-us

UA-CPU: x86

Proxy-Connection: Keep-Alive

User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; IEMB3; .NET CLR 2.0.50727; IEMB3)

Host: www.google.com

Cookie: PREF=ID=f685dc26bb332848:TM=1234999965:LM=1234999965:S=R1r_jIqtuS1FxLKY; NID=19=GXzMU2_xbI1FEDE271qoPk995wncwEEkwWZ6kNnksvjPsFacBMJ7phMuR3Z7J-Ozmw32-JEX4cTdmUcdwxV34uJagvS0upWzLDTM2Xw_u6-7JxcQcwaXSZaS0PdeTcUq; BCSI-CSCC4F542D=2

 

Working through different proxy running same SG OS 4.2.8.6 GET http://www.google.com/trends?q=annka+sorenstam,+michelle+wie HTTP/1.1

Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/x-silverlight, */*

Accept-Language: en-us

Accept-Encoding: gzip, deflate

User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; InfoPath.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648)

Host: www.google.com

Proxy-Connection: Keep-Alive