Forum Discussion
How to preserve HTTP headers for HTTP::respond
I need to preserve HTTP headers for HTTP::respond, I tried the following approach
when HTTP_RESPONSE {
if {[HTTP::has_responded]} {return}
catch { unset hdrs }
foreach header [HTTP::header names] {
lappend hdrs $header "[HTTP::header $header]"
}
log local0. "Headers: $hdrs"
HTTP::respond 301 -version auto $hdrs
}
Headers appear properly in the log, but I don't receive them in the response, only Connection Content-Length and Server are populated
Don't see errors either. What did I miss?
Thanks,
Vadym
- Simon_BlakelyEmployee
Vadym,
HTTP::respond does not allow variables to be expanded and evaluated in the context of the command execution.
You will need to use eval. However, this introduces the risk of a TCL injection vulnerability.
when HTTP_RESPONSE { if {[HTTP::has_responded]} {return} catch { unset hdrs } foreach header [HTTP::header names] { lappend hdrs $header "[HTTP::header $header]" } log local0. "Headers: $hdrs" eval HTTP::respond 301 -version auto $hdrs }
You may also need to play with quoting the values.
Hello Simon
Tried this approach for modified Exchange iRule to logout user and sometimes I caught connection reset inside browser (but there is no TCL error inside LTM logs). So I cannot understand why "eval {}" with variable leads to connection errors compared with regular HTTP::respond header1 value1 header2 value2 ...
My code
when RULE_INIT priority 500 { set static::hdrs [list \ "\"Location\" \"/vdesk/hangup.php3\"" \ "\"Content-Type\" \"text/html\"" \ "\"Cache-Control\" \"no-cache, must-revalidate\"" \ "\"Set-Cookie\" \"MRHSession=deleted;expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"LastMRH_Session=deleted;expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"cadata=null;Expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"ClientId=null;Expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"UC=null;Expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"X-BackEndCookie=null;Expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ "\"Set-Cookie\" \"X-OWA-CANARY=null;Expires=Thu, 01-Jan-1970 00:00:00 GMT;path=/;secure\"" \ ] } when HTTP_REQUEST priority 500 { ... eval {HTTP::respond 302 -version 1.1 noserver "[join $static::hdrs]"} ... } when ACCESS_SESSION_STARTED priority 500 { ... eval {ACCESS::respond 302 -version 1.1 noserver "[join $static::hdrs]"} ... }
Do you know maybe there are some gotchas that should be included in the code?
- Vadym_ChepkovNimbostratus
Thank you, , it helped. Is it enough to put $hdrs in curly braces to avoid TCL injection ?
Or maybe append HTTP::respond statement with an additional header? Article doesn't provide detailed recommendation how to protect from malicious input.
Also, I solved the problems of quoting by converting $hdrs to a list, i.e.
set headers {} foreach header [HTTP::header names] { lappend headers $header [HTTP::header value $header] }
Thanks,
Vadym
- Simon_BlakelyEmployee
>Is it enough to put $hdrs in curly braces to avoid TCL injection ?
No - that just makes {$hrds} a single parameter with spaces in it.
I suspect you need to individually wrap each element (the headers and the values) in curly braces prior to the eval
So you end up doing an eval on
HTTP::respond 301 -version auto {header1} {header1_value} {header2} {header2_value} ...
That prevents eval from further expanding the strings in the curly braces.
But I don't really get TCL injection either - I know it is possible via unsanitized input, and eval is a common problem, and curly braces help, but I still struggle with it.
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