Advisory: Cross-site Scripting in Securimage 3.6.2
RedTeam Pentesting discovered a cross-site scripting (XSS) vulnerability
in the Securimage CAPTCHA software, which allows attackers to inject
arbitrary JavaScript code via a crafted URL.
### Details
- Product: Securimage
- Affected Versions: \>= 3.2RC1
- Fixed Versions: 3.6.4
- Vulnerability Type: Cross-site Scripting
- Security Risk: high
- Vendor URL: `https://www.phpcaptcha.org/`
- Vendor Status: fixed version released
- Advisory URL: `https://www.redteam-pentesting.de/advisories/rt-sa-2016-002`
- Advisory Status: published
- CVE: GENERIC-MAP-NOMATCH
- CVE URL: `https://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH`
### Introduction
"Securimage is an open-source free PHP CAPTCHA script for generating
complex images and CAPTCHA codes to protect forms from spam and abuse.
It can be easily added into existing forms on your website to provide
protection from spam bots. It can run on most any web server as long as
you have PHP installed, and GD support within PHP. Securimage does
everything from generating the CAPTCHA images to validating the typed
code. Audible codes can be streamed to the browser with Flash for the
vision impaired."
(from the project's homepage)
### More Details
The Securimage download package and GitHub repository include several
example scripts to demonstrate the usage of the library. Among these
scripts is the file example_form.ajax.php. It returns JavaScript code
that includes an unencoded value from the variable \$\_SERVER\['PHP_SELF'\]
directly embedded into the website.
In Securimage versions from 3.2RC1 to 3.5 the following code is
vulnerable:
```
function processForm()
{
new Ajax.Request('', {
method: 'post',
parameters: $('contact_form').serialize(),
onSuccess: function(transport) {
```
In Securimage versions from 3.5.2 to 3.6.2 the following code is
vulnerable:
```
function processForm()
{
jQuery.ajax({
url: '',
type: 'POST',
data: jQuery('#contact_form').serialize(),
dataType: 'json',
}).done(function(data) {
```
The problem here is that the value of the variable \$\_SERVER\['PHP_SELF'\]
can, depending on the configuration of the web server, often be
manipulated by an attacker to include special characters like
apostrophes.
### Proof of Concept
The following URL can be used to demonstrate the vulnerability for
Securimage versions from 3.2RC1 to 3.5 on with a vulnerable web server
configuration:
`http://www.example.com/example_form.ajax.php/`');}alert('RedTeam Pentesting');a=function(){a('
Securimage versions from 3.5.2 to 3.6.2 can be exploited with the
following URL:
`http://www.example.com/example_form.ajax.php/`'});}alert('RedTeam Pentesting');a=function(){a({x:'
The result is a notification showing the text "RedTeam Pentesting". The
value of the variable \$\_SERVER\['PHP_SELF'\] is embedded in verbatim into
the HTML source code of the resulting web page.
### Workaround
The file example_form.ajax.php should be deleted from the Securimage
directory on a web server.
### Fix
Update to version 3.6.4.
### Security Risk
This security vulnerability is rated as a high risk. It allows executing
arbitrary JavaScript code in users' browsers if they access URLs
prepared by attackers. This provides many possibilities for further
attacks against these users. Since Securimage is usually used as a
software library to provide CAPTCHA functionality for web applications,
the vulnerability could be used to exploit all web applications hosted
on the same domain.
### Timeline
- 2016-02-03 Vulnerability identified
- 2016-02-12 Customer approved disclosure to vendor
- 2016-02-23 CVE number requested
- 2016-02-24 CVE number not assigned, "non-prioritized product"
- 2016-03-02 Vendor contacted
- 2016-03-03 Vendor releases fixed version
- 2016-03-22 Advisory released
### References
### RedTeam Pentesting GmbH
RedTeam Pentesting offers individual penetration tests performed by a
team of specialised IT-security experts. Hereby, security weaknesses in
company networks or products are uncovered and can be fixed immediately.
As there are only few experts in this field, RedTeam Pentesting wants to
share its knowledge and enhance the public knowledge with research in
security-related areas. The results are made available as public
security advisories.
More information about RedTeam Pentesting can be found at: