In early 2023, Microsoft patched a critical security flaw tracked as CVE-2023-21726. This vulnerability resides in the Windows Credential Manager's user interface and, if exploited, can let an attacker get higher privileges than they should — potentially giving them the keys to your kingdom.

This deep-dive aims to demystify CVE-2023-21726, show sample code, and explain exactly *how* an attacker could work it. Whether you’re a sysadmin, developer, or just a Windows power-user, this guide breaks it down in plain language.

What Is Windows Credential Manager?

The Credential Manager in Windows stores usernames and passwords. It gives apps a secure (well, mostly!) way to save secrets you don’t want to type every time.

Usually, you need administrative permission to view saved credentials of other users or system accounts. The user interface (UI) ensures you can’t just “see all passwords.”

But what if there’s a bug in the UI logic? Hello, CVE-2023-21726.

CVE-2023-21726 is an *Elevation of Privilege (EoP)* flaw. Microsoft said

> An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.

How does this happen?

By leveraging a flaw in the Credential Manager interface, a local attacker could trick Windows into running a process *as SYSTEM* — the highest-level account.

For a successful attack, all the attacker needs is the ability to log into the target system. No special access or complex network tricks required.

Here’s a distilled explanation

1. There’s an issue when Credential Manager prompts for credentials. It spawns a process that should *not* inherit admin rights by accident.

Below is a simplified PoC (conceptual: for illustration, not an actual weaponized exploit)

# Save as exploit-CVE-2023-21726.ps1
# Goal: Leverage flaw for SYSTEM-level process spawn

# 1. Use schtasks to create a SYSTEM-level task that runs our payload
schtasks /Create /SC ONCE /TN "sys-cmd" /TR "cmd.exe" /ST 23:59 /RU SYSTEM

# 2. Trigger the task
schtasks /Run /TN "sys-cmd"

# 3. If not patched, we might get spawned as SYSTEM

Or, using the Windows API (in C)

// Conceptual code: Manipulate how Credential Manager launches UI process

#include <windows.h>
#include <stdio.h>

int main() {
    // Trick Credential Manager to spawn a process in SYSTEM context
    // (Note: Details omitted for safety)
    // exploit logic would go here...
    printf("Attempt privilege escalation via CVE-2023-21726...\n");
    // Launch cmd.exe as SYSTEM (if vulnerable)
    system("whoami");
    return ;
}

Real exploits may look different and use more subtle methods to interact with the UI process. Official PoCs are kept private for security reasons, but check references at the end for academic details.

Gain SYSTEM shell (run code as SYSTEM)

- Read/write system files

Extract plaintext passwords from system

It’s like sitting in the pilot’s seat — no passwords needed.

All supported Windows versions prior to February 2023’s Patch Tuesday.

If you haven’t updated lately, you might still be vulnerable.

How to Stay Safe

Patch immediately!  
Microsoft released updates in February 2023. Get them via Windows Update, or see the links below.

- Microsoft Security Response Center: CVE-2023-21726
- NIST NVD CVE-2023-21726 Details
- Microsoft Patch Tuesday Notes – February 2023

Security research write-ups

- KernelMode.info forum: Discussion of Windows EoP CVEs
- Analysis by Rapid7 Labs

Conclusion

CVE-2023-21726 is a reminder that even UI bugs can have deep consequences. With a simple misstep in how a window and its security tokens are handled, attackers could go from zero to SYSTEM. If you run a Windows device — personal or in big IT — patch up, and remember that the UI is not just eye candy; it’s a guardian of your secrets.

Stay safe! If you want more breakdowns of critical CVEs, follow this blog for exclusive insights.

Timeline

Published on: 01/10/2023 22:15:00 UTC
Last modified on: 01/18/2023 15:43:00 UTC