TYPO3 Formhandler 2.4.0 Cross Site Scripting

Type packetstorm
Reporter redteam-pentesting.de
Modified 2017-07-27T00:00:00


                                            `Advisory: Cross-Site Scripting in TYPO3 Formhandler Extension  
RedTeam Pentesting discovered a cross-site scripting vulnerability (XSS)  
in the TYPO3 extension Formhandler.  
Product: TYPO3 Formhandler  
Affected Versions: 2.4.0 and probably earlier  
Fixed Versions: none, project no longer maintained  
Vulnerability Type: Cross-site scripting  
Security Risk: medium  
Vendor URL: http://www.typo3-formhandler.com/formhandler/  
Vendor Status: patch available  
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2016-007  
Advisory Status: published  
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH  
TYPO3 Formhandler is an extension to build and handle forms on TYPO3  
More Details  
TYPO3 Formhandler can validate form data and create a pre-filled form  
with previous values and error messages, if the data does not comply.  
It uses input sanitisation and output encoding as an approach to prevent  
XSS when embedding the values in the resulting web page. Input  
sanitisation happens in the function "sanitizeValues()" defined in  
Classes/Interceptor/RemoveXSS.php line 62ff.[0]:  
* This method does XSS checks and escapes malicious data  
* @param array $values The GET/POST parameters  
* @return array The sanitized GET/POST parameters  
public function sanitizeValues($values)  
if (!is_array($values)) {  
return [];  
foreach ($values as $key => $value) {  
$value = \TYPO3\CMS\Core\Utility\GeneralUtility::removeXSS($value);  
The function removeXSS() is deprecated in TYPO3 version 8 [1] and  
contains a known vulnerability for user-assisted XSS [2].  
TYPO3 Formhandler also supports a templating system that uses place  
holders that are delimited with three hash-signs, for example:  
Some of these values are user-controlled but not all of them are  
properly encoded. For example the auth code is used as follows (see  
Classes/View/Form.php, line 519ff.):  
if ($this->gp['generated_authCode']) {  
$markers['###auth_code###'] = $this->gp['generated_authCode'];  
But other markers are encoded via htmlspecialchars() (line 513ff):  
$markers['###HIDDEN_FIELDS###'] .= '  
<input type="hidden" ' . $hiddenActionFieldName . ' id="ieHiddenField-' . htmlspecialchars($this->gp['randomID']) . '" value="1" />  
Another value that TYPO3 Formhandler uses in forms is a so-called random  
ID, that is also obtained from a URL or POST parameter. In combination,  
both parameters allow to bypass the removeXSS() function as well and  
allow XSS.  
Proof of Concept  
The proof-of-concept URLs are created for the basic file upload example  
provided by the TYPO3 Formhandler documentation page [3]. The examples  
set the random ID parameter to a value containing the place holder  
###auth_code### that contains an additional attack vector. For the  
attack vector to be included, the URLs need to be called twice. The  
second request needs to include the PHP session cookie that was set in  
response to the first request.  
In the first example, the auth code bypasses the input sanitisation by  
using the placeholder ####### that renders to the empty string:  
In the second example, the XSS code is split between the random ID and  
the auth code. The auth code is:  
"><img src=x on  
And the random ID is:  
###auth_code###error='alert(/RedTeam Pentesting/.source)'  
The third example uses the known bypass for the removeXSS() function by  
setting the auth code to:  
"/><a href="data:text/html;base64,PHNjcmlwdD5hbGVydCgiUmVkVGVhbSBQZW50ZXN0aW5nIik8L3NjcmlwdD4K">XSS</a>  
And using it as the random ID.  
A possible workaround might be to patch Classes/View/Form.php to apply  
htmlspecialchars() before storing the auth code value for the respective  
marker. An unofficial patch from the vendor is available at:  
None, since the project is no longer maintained.  
Security Risk  
Attackers can use the vulnerability to execute arbitrary JavaScript on  
the target system. Depending on the site it can be used to use and  
monitory the session of users, present phishing forms or harm the site's  
reputation with false information. Attackers need to get people to open  
the respective URLs twice for this attack to work and therefore can only  
target individual users. All in all this is considered to be a  
medium-risk vulnerability. Depending on the affected site the risk needs  
to be adjusted accordingly.  
2016-09-22 Vulnerability identified  
2016-10-07 Customer approved disclosure to vendor  
2016-10-07 Vendor notified  
2016-10-11 Preliminary advisory sent to vendor  
2016-10-12 Vendor prepared patch and sent it to TYPO3 security team  
2016-10-13 Customer needs time to test the patch and deploy it  
2017-07-10 Customer finished testing and deployment of patch  
2017-07-17 Vendor agreed to have patch published as PR on Github  
2017-07-27 Vendor patch published as pull request for a possibly active fork  
2017-07-27 Advisory released  
[0] https://github.com/reinhardfuehricht/typo3-formhandler/blob/master/Classes/Interceptor/RemoveXSS.php#L63  
[1] https://docs.typo3.org/typo3cms/extensions/core/8-dev/Changelog/8.2/Deprecation-76164-DeprecateRemoveXSS.html  
[2] https://packetstormsecurity.com/files/137127/typo3-xssbypass.txt  
[3] http://examples.typo3-formhandler.com/start/  
RedTeam Pentesting GmbH  
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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  
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RedTeam Pentesting GmbH Tel.: +49 241 510081-0  
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