CVE-2023-28250 - Unveiling the PGM Remote Code Execution Vulnerability in Windows

In April 2023, Microsoft patched an alarming vulnerability, CVE-2023-28250, that struck at the core of Windows networking: the Pragmatic General Multicast (PGM) protocol. This bug allowed attackers to execute their own code remotely — potentially taking control of vulnerable systems… with little more than a network packet. If you run enterprise-grade Windows, or are just interested in behind-the-scenes Windows security, this exclusive long read will tell you what happened, why it was a big deal, and the technical details — with code snippets and real-world references.

What is PGM and Why Should You Care?

PGM (Pragmatic General Multicast) is a rarely-used Windows protocol for one-to-many data delivery. It’s particularly relevant in financial trading, cluster computing or messaging scenarios where the same data is sent to many machines. Support for PGM sits deep in Windows, specifically in the “PGM.sys” driver.

Most users never know it’s there; but if you’re running MSMQ (Microsoft Message Queuing), part of Exchange, some SQL Server features, or clustered services, the code is probably active and listening on your network.

What is CVE-2023-28250?

CVE-2023-28250 is a remote code execution (RCE) bug, found and responsibly disclosed by security researcher Yuki Chen (Project Zero). The vulnerability is due to improper handling of memory in PGM.sys when handling specially crafted network packets. An attacker who sends a malicious packet could force a use-after-free scenario, which allows the attacker to execute code with kernel privileges — the highest level!

How Does It Work? (Explained Simply)

The core bug is a classic *use-after-free* in the PGM driver.

Attacker crafts special packet to interact with the PGM subsystem.

2. The driver frees a memory object in response, but keeps using a pointer to that now-invalid memory area.
3. The attacker follows up with additional data (or just waits), and the system may now use that invalid (and possibly attacker-controlled) memory.
4. Because PGM.sys runs in the Windows kernel, the attacker’s payload would execute with SYSTEM-level permissions.

This is not a rare browser crash, but a high-impact, deep OS exploit!

A Closer Look: Code Snippet & Exploit Flow

Let’s simulate the logic behind this bug. (This isn’t the real Windows source code, which isn’t public, but it’ll help explain):

// Pseudo-code from a vulnerable memory freeing scenario in a network driver
struct pgm_session *session = find_pgm_session(packet);

if (session) {
    if (malicious_packet(packet)) {
        free(session); // Frees the session
        // ... some operations ...
        process_session(session); // Uses the same pointer! Use-After-Free!
    }
}

In the real-world exploit, an attacker would

How Was it Found? What Was Patched?

Google Project Zero researchers actively hunt such deep-bugs. In this case, Yuki Chen’s bug report highlights the fuzzing of network protocols and identifies the exact flaw.

Microsoft’s Security Update Guide for CVE-2023-28250 details the patched versions and acknowledges the high severity (CVSS 9.8!).

The fix? Microsoft updated the driver to not reuse memory pointers after freeing them, closing the door on attackers.

Exploit Scenario in the Wild

Imagine your network exposes the MSMQ service, which uses PGM. An unauthenticated user on the same network or via a VPN could send a malicious packet to the vulnerable port (usually TCP port 1801, but PGM uses its own protocol over IP).

Praetorian Labs demonstrated a similar attack scenario here, although for a different CVE, the exploitation path is similar — packet in, code run.

While, as of now, public exploits are not widespread, proof-of-concept code was quickly developed by skilled researchers (see madscientistsguild/poc-cve-2023-28250), and Metasploit support may follow.

How to Protect Yourself

- Update your Windows systems NOW. If you run any Windows with MSMQ or enable PGM.sys, patching quickly is essential.

Turn off unnecessary MSMQ or PGM support if it isn’t needed (feature optional in Windows).

- Block untrusted network access around port 1801 and IGMP/PGM network traffic.

Monitor for abnormal kernel memory behavior using EDR tools.

Patch details:

April 2023 Patch Tuesday

- Supported systems: Windows 10/11, Server 2016/2019, and others

References & Further Reading

- Microsoft Security Advisory CVE-2023-28250
- Project Zero Analysis by Yuki Chen
- MSDN: PGM Protocol Overview
- MSRC CVE Description
- PoC on GitHub
- Qualys QSA-23-11: Analysis of Related MSMQ Vulnerabilities

Conclusion

CVE-2023-28250 is not just another bug — it’s a rare window into the sensitive “underbelly” of Windows networking. A decades-old protocol, still hanging around in modern systems, suddenly becomes a high-profile attack surface due to a kernel flaw. Security researchers proved that every line of code matters, even the old forgotten ones. If you run enterprise systems, this is your wake-up call: update, audit, and keep an eye on those “optional” services!

Timeline

Published on: 04/11/2023 21:15:00 UTC
Last modified on: 04/13/2023 01:10:00 UTC