CVE-2026-6520: Wireshark OpenFlow DoS Vulnerability

CVE-2026-6520 Overview

CVE-2026-6520 is a denial of service vulnerability affecting Wireshark's OpenFlow v6 protocol dissector. The vulnerability allows an attacker to cause an infinite loop condition when Wireshark processes specially crafted network traffic, resulting in the application becoming unresponsive and consuming excessive system resources.

Critical Impact
Attackers can crash or hang Wireshark installations by sending malicious OpenFlow v6 protocol packets, disrupting network analysis and security monitoring operations.

Affected Products

Wireshark 4.6.0 to 4.6.4
Wireshark 4.4.0 to 4.4.14

Discovery Timeline

2026-04-30 - CVE-2026-6520 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-6520

Vulnerability Analysis

This vulnerability is classified under CWE-835 (Loop with Unreachable Exit Condition), commonly known as an infinite loop vulnerability. The flaw exists within the OpenFlow v6 protocol dissector component of Wireshark, which is responsible for parsing and analyzing OpenFlow protocol traffic during packet capture analysis.

When Wireshark encounters maliciously crafted OpenFlow v6 packets, the dissector enters a loop condition that lacks a proper exit mechanism. This causes Wireshark to become unresponsive as it continuously processes the malformed data without terminating. The local attack vector requires user interaction, specifically that a user must open a malicious capture file or actively capture traffic containing the exploit payload.

The vulnerability impacts the availability of the affected system by consuming CPU resources indefinitely until the Wireshark process is forcibly terminated.

Root Cause

The root cause is an infinite loop condition (CWE-835) in the OpenFlow v6 protocol dissector. The dissector fails to properly validate or handle certain malformed packet structures, resulting in a loop that never reaches its exit condition. This type of vulnerability typically occurs when parsing routines do not adequately check for boundary conditions or malformed input that could cause iteration counts to never decrement or termination conditions to never be satisfied.

Attack Vector

The attack requires local access and user interaction to exploit. An attacker must deliver a malicious packet capture file (.pcap, .pcapng) to the victim or position themselves on a network segment where the victim is actively capturing traffic. When the victim opens the malicious capture file or captures the malicious OpenFlow v6 traffic, Wireshark's dissector enters an infinite loop.

The vulnerability mechanism involves sending specially crafted OpenFlow v6 protocol data that triggers the flawed parsing logic. For detailed technical information about the specific packet structures involved, refer to the Wireshark Security Advisory WNPA-SEC-2026-40 and the GitLab Wireshark Work Item.

Detection Methods for CVE-2026-6520

Indicators of Compromise

Wireshark process consuming 100% CPU on a single core and becoming unresponsive
Presence of .pcap or .pcapng files containing malformed OpenFlow v6 protocol data
User reports of Wireshark hanging when opening specific capture files
Network capture files received from untrusted sources containing OpenFlow protocol traffic

Detection Strategies

Monitor for Wireshark processes that consume excessive CPU resources for extended periods
Implement file integrity monitoring for capture file directories to identify potentially malicious files
Use process monitoring to detect hung Wireshark instances that require forced termination
Review network capture file sources and implement policies against opening untrusted capture files

Monitoring Recommendations

Deploy endpoint detection and response (EDR) solutions to monitor for abnormal Wireshark process behavior
Configure alerts for processes entering high CPU utilization states without network I/O activity
Implement application whitelisting policies that restrict execution of older, vulnerable Wireshark versions
Monitor system logs for repeated Wireshark crash events or forced terminations

How to Mitigate CVE-2026-6520

Immediate Actions Required

Upgrade Wireshark to version 4.6.5 or later for the 4.6.x branch
Upgrade Wireshark to version 4.4.15 or later for the 4.4.x branch
Avoid opening packet capture files from untrusted or unknown sources
Consider disabling the OpenFlow v6 dissector if not required for analysis workflows

Patch Information

Wireshark has released security patches addressing this vulnerability. Users should update to the latest stable release in their respective version branch. For detailed patch information and download links, consult the Wireshark Security Advisory WNPA-SEC-2026-40.

Additional technical details about the fix can be found in the GitLab Wireshark Work Item.

Workarounds

Disable the OpenFlow v6 protocol dissector through Wireshark's protocol preferences until patching is complete
Use TShark with protocol filtering to exclude OpenFlow dissection when processing untrusted captures
Implement network segmentation to limit exposure to potentially malicious OpenFlow traffic
Process untrusted capture files in isolated virtual environments to contain any denial of service impact

bash

# Disable OpenFlow v6 dissector in Wireshark preferences
# Navigate to: Analyze -> Enabled Protocols
# Search for "openflow" and uncheck to disable

# Alternative: Use TShark with protocol filter to exclude OpenFlow
tshark -r capture.pcap --disable-protocol openflow_v6