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Trend Micro reported this vulnerability to Microsoft after observing Void Banshee APT exploitation in the wild; the zero-day attack hinged on the premise that MHTML links would automatically open in the old Internet Explorer engine. Within the old engine context, HTA files will prompt to open by default, facilitating easier code execution. The threat actors were observed appending many spaces to the file name to misrepresent the secondary HTA file as a PDF in the IE pop-up box. Additionally, Check Point researcher Haifei Li is credited for a report that resulted in a “Defense-in-depth” patch for this chain, which is probably related to the HTA file name misrepresentation trick.

The process of exploitation would typically look like this:

• An attacker site is visited or a phishing message is sent to the victim.
  
• The victim downloads a malicious “.url” file that masquerades as a legitimate document.
  
• The victim clicks the “.url” payload, opening the embedded “mhtml:” link and launching Internet Explorer.
  
• The IE engine prompts the user to open the second-stage HTA file.
  
• The victim clicks “open” on the pseudo-PDF prompt.
  
• The victim clicks “Allow” on the IE security prompt for the “HTML Application host” execution.
  

In summary, the intent of this attack chain is to misrepresent and remove some security hurdles for malware execution on Windows. Successful exploitation does still require quite a bit of clicking through prompts by the user. However, this is likely enough to significantly increase execution numbers for the affiliated malware campaign, which was reported to be deploying information stealers.

Description

Missing Sanitization of $item->getGroup() (lines 864 and 1269) in fieldcollectionTreeAction/objectbrickTreeAction functions in bundles/AdminBundle/Controller/Admin/DataObject/ClassController.php allows Admin User to perform Source Code Injection through Stored Group Fields (in Object Bricks/Field Collection under settings module) resulting in Information Exposure (cookie theft).

Analysis

What makes this vulnerability stored is that the Group fields (for the listings under Object Bricks or Field Collection in the Settings Module) are saved to the database in the objectbrickUpdateAction function (serves the route /objectbrick-update for the methods {“PUT”, “POST”}).

Example of the PUT request: https://demo.pimcore.com/admin/class/objectbrick-update

That means the patch only mitigates the XSS in the objectbrickTreeAction function (serves the route /objectbrick-tree for the methods={“GET”, “POST”}).

Example of the GET request: https://demo.pimcore.com/admin/class/objectbrick-tree?_dc=1721102886220&grouped=1&node=0

The execution would happen in the Object Bricks/Field Collection listings for Data Objects in the Settings Module (span with class x-tree-node-text in a table with id treeview-record)

Rating

The attack is relatively straightforward (XSS payloads are well documented and relatively easy to craft), requiring low privileges (anyone could access the Demo with privileged permissions and target other active users) and minimal complexity, though user interaction is needed.
The vulnerability can lead to limited data exposure and modification but does not significantly impact availability. Since the Demo resets every two hours (restoring all data to the default state), it is minimally valuable.

This vulnerability also requires authentication, but any SharePoint user with Site Owner permissions can hit it. However, the default configuration of SharePoint allows authenticated users to create sites. That’s why I disagree with Microsoft’s CVSS rating here. By changing “Privileges Required” to low instead of high, it takes it from a 7.2 to (IMHO) more accurate 8.8

The POC disclosed shows up the easy exploitation despite to be authenticated.