buglwIP - A Lightweight TCP/IP stack - Bugs: bug #56197, HTTPD SSI handler does not handle...


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bug #56197: HTTPD SSI handler does not handle character sequence /< properly

Submitted by:  Matthias Dietrich <mdietrich>
Submitted on:  Tue 23 Apr 2019 12:06:00 PM UTC  
Category:  apps Severity:  3 - Normal
Item Group:  Faulty Behaviour Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open Planned Release:  None
lwIP version:  Other

Mon 06 May 2019 12:43:53 PM UTC, comment #2: 

Sure. Actually I could have sent a patch with the bug report, but the thing is, I am not using the current HEAD version in my project right now, so I was not sure how you want to proceed.
But yes, I can provide a patch.

Matthias Dietrich <mdietrich>
Mon 06 May 2019 10:26:51 AM UTC, comment #1: 

Can you provide a (tested ;-) ) patch that works on your system?

Dirk Ziegelmeier <dziegel>
Project Administrator
Tue 23 Apr 2019 12:06:00 PM UTC, original submission:  

The httpd server supports two sets of SSI markers ('<!--#' and '/*#'). Unfortunately, the parsing function does not handle properly the case where a character sequence starts with characters of one marker and continues with the first character of another marker.

Example: <img src="images/<!--#PicDevice-->.png" />

When the parser hits the first '/' character, it changes its state from TAG_NONE to TAG_LEADIN, as '/' could be the start of the '/*#' marker. The parser then moves to the next character ('<'). The state machine now checks whether this character ('<') matches the '/*#' marker. As this is not the case, the state is switched back to TAG_NONE and the parser moves to the next character ('!'). Unfortunenately, we have now lost the possibility of checking whether '<' was the start of a marker.

in the state "TAG_LEADIN", only move to the next character
in the stream when we have found a matching character,
otherwise just change the state back to TAG_NONE but do not
increase ssi->parsed. This allows to parse again the current character and detect the start of another marker.

Matthias Dietrich <mdietrich>


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