CVE-2023-21682 - Unpacking Windows Point-to-Point Protocol (PPP) Information Disclosure Vulnerability

In early 2023, Microsoft patched several security flaws. Among them was CVE-2023-21682, a Windows Point-to-Point Protocol (PPP) Information Disclosure Vulnerability. While this wasn’t the year’s flashiest bug, it’s important because vulnerabilities in PPP may spill sensitive system memory, leading to further system compromise.

Today, we’ll break down CVE-2023-21682: from what it is, to real-world impact, to illustrating how an attacker might leverage this flaw, step-by-step. We’ll keep technical explanations digestible, share code samples, and link to authoritative sources.

What is PPP, and Why Does It Matter?

PPP is a network protocol used for establishing internet links over serial connections—think dial-up, VPNs, and some broadband. It packages and transports data between two nodes, such as your PC and your ISP.

If PPP mishandles data—like failing to properly sanitize a buffer before sending it across the wire—sensitive information from system memory (usernames, passwords, or cryptographic keys) might get leaked.

Vulnerability Type: Information Disclosure

- CVE ID: CVE-2023-21682

PPP protocol processes data sent by a remote attacker over a PPP connection.

2. Due to improper handling of certain PPP packets, memory from the victim system is copied into the response.

PoC – Simulating the Flaw

While Microsoft hasn’t released technical details, the vulnerability closely resembles prior PPP ‘leak’ bugs. We’ll use a generic demonstration to show how these flaws might play out.

Assume an attacker can initiate a PPP connection to a Windows system (rare, but not impossible in real environments). Let’s simulate how an improperly implemented PPP handler may leak memory:

// WARNING: This is a theoretical example, not actual Windows code

#define PPP_PACKET_SIZE 2048
char buffer[PPP_PACKET_SIZE];
memset(buffer, , PPP_PACKET_SIZE);               // Secure: Zero out buffer

if (should_fill_with_data()) {
    fill_with_ppp_data(buffer);
} else {
    // Oops: buffer still has whatever (potentially sensitive) data was left in stack memory!
    // In the buggy case, this line is missing.
}

send_over_ppp(connection, buffer, PPP_PACKET_SIZE);

In vulnerable code, forgetting memset() leaves random chunks of memory—which could contain authentication credentials or other sensitive data—inside outbound PPP packets.

Attacker connects to vulnerable Windows system (e.g., via VPN or direct dial-up using PPP).

2. Sends malformed/invalid PPP packets, triggering the system to respond with a buffer that hasn't been sanitized.
3. Receives the reply containing blocks of uninitialized memory—possibly including data from prior connections, system logs, or even session credentials.
4. Repeats the process to collect more leaked memory chunks, potentially reconstructing sensitive information.

Code Snippet: Sending Malformed PPP Packet (Python Example)

Below is a Python example using scapy for educational purposes only.

from scapy.all import *

# Build a PPP LCP echo request with extra payload (simulate triggering a bug)
pkt = Ether()/PPP()/PPP_LCP(code=9, id=42, data=b"\x00" * 150)

# Normally, you'd need a PPP session. This is illustrative; real exploitation involves lower-level access.

sendp(pkt, iface="ppp")

*Note: This will only work if your machine is actually connected with PPP and you're cleared to test it!*

Systems allowing remote PPP access: legacy VPNs, dial-up modems, or direct serial connections.

- Attackers must be authenticated or able to establish PPP sessions—this greatly lowers widespread risk but makes the bug serious in high-security environments.

Possible exposure of credentials, security tokens, or kernel memory.

- Chaining information disclosure with other bugs (like privilege escalation) can lead to much broader compromise.

Apply Microsoft’s patch released January 2023.

- Microsoft Security Response Center Advisory

References & Further Reading

- Microsoft Patch Advisory - CVE-2023-21682
- NVD Details - CVE-2023-21682
- CISA Alert on Microsoft Patch Tuesday, January 2023
- Reference example vulnerabilities: Talos Advisory on PPP Leaks

Conclusion

CVE-2023-21682 reminds us that even “old” technologies like PPP can hide modern threats. While not flashy, information disclosure bugs form the backbone of major attacks when paired smartly by skilled adversaries. Even if you never use PPP, understanding and patching these bugs keeps your environment safer from unexpected angles.

Patch promptly. Audit unused legacy services. Stay vigilant.

If you want to deep dive or have questions, drop your comments below or check out the referenced advisories for official details.


*Exclusive for readers who want the inside scoop on Microsoft’s lesser-known flaws!*

Timeline

Published on: 01/10/2023 22:15:00 UTC
Last modified on: 01/18/2023 16:07:00 UTC