Advisory:           Cross-Site Scripting vulnerability in Nagios
Advisory ID:        SSCHADV2011-002
Author:             Stefan Schurtz
Affected Software:  Successfully tested on: nagios-3.2.0 / nagios-3.2.3
Vendor URL:         http://www.nagios.org
Vendor Status:      0000207: Cross-Site Scripting vulnerability in Nagios 
CVE-ID:  	    2011-1523
OSVDB-ID: 	    71059

==========================
Vulnerability Description:
==========================

This is Cross-Site Scripting vulnerability

JavaScript can be included in style sheets by using "expression()" (IE only)

==================
Technical Details:
==================

The function "strip_html_brackets" strip > and < from string but itīs not enough to prevent XSS attacks in "statusmap.cgi&layer="

http://site/nagios/cgi-bin/statusmap.cgi?layer=' style=xss:expression(alert('XSS')) '
http://site/nagios/cgi-bin/statusmap.cgi?layer=' onmouseover="alert('XSS')" '

-----------
cgiutils.c
-----------

[schnipp]
.
.
/* strip > and < from string */

void strip_html_brackets(char *buffer){
        register int x;
        register int y;
        register int z;

        if(buffer==NULL || buffer[0]=='\x0')
                return;

        /* remove all occurances in string */
        z=(int)strlen(buffer);
        for(x=0,y=0;x<z;x++){
                if(buffer[x]=='<' || buffer[x]=='>')
                        continue;
                buffer[y++]=buffer[x];
                }
        buffer[y++]='\x0';

        return;
        }
.
.
[schnapp]

-----------
statusmap.c
-----------

[schnipp]
.
.
/* we found the layer argument */
         else if(!strcmp(variables[x],"layer")){
                x++;
                if(variables[x]==NULL){
                      error=TRUE;
                      break;
                }

                strip_html_brackets(variables[x]);
                add_layer(variables[x]);
                }
.
.
[schnapp]

-----------
Problem in "statusmap.c"
-----------

[schnipp]
.
.
/* print layer url info */
void print_layer_url(int get_method){
        layer *temp_layer;

        for(temp_layer=layer_list;temp_layer!=NULL;temp_layer=temp_layer->next){
                if(get_method==TRUE)
                        printf("&layer=%s",temp_layer->layer_name); <-- no "escape_string"
                else
                        printf("<input type='hidden' name='layer' value='%s'>\n",escape_string(temp_layer->layer_name));
                }
.
.
[schnapp]

=========
Solution:
=========

if(get_method==TRUE)
          /* printf("&layer=%s",temp_layer->layer_name); */
          printf("&layer=%s",escape_string(temp_layer->layer_name));

====================
Disclosure Timeline:
====================

09-Mar-2011 - informed developers
09-Mar-2011 - post on Nagios Tracker - http://tracker.nagios.org/view.php?id=207
09-Mar-2011 - Release date of this security advisory
10-Mar-2011 - post on BugTraq - 

========
Credits:
========

Vulnerability found and advisory written by Stefan Schurtz.

===========
References:
===========

http://www.nagios.org
http://www.rul3z.de/advisories/SSCHADV2011-002.txt
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2011-1523
http://www.tenable.com/plugins/index.php?view=single&id=55163