CVE-2026-6521: Wireshark OpenFlow v5 DoS Vulnerability

CVE-2026-6521 Overview

CVE-2026-6521 is a denial of service vulnerability affecting the OpenFlow v5 protocol dissector in Wireshark network protocol analyzer. The vulnerability allows attackers to trigger infinite loops in the dissector, causing the application to become unresponsive when processing specially crafted network traffic or capture files. This vulnerability is classified as CWE-835 (Loop with Unreachable Exit Condition).

Critical Impact
An attacker can cause Wireshark to hang indefinitely by providing malicious OpenFlow v5 protocol data, disrupting network traffic analysis operations and potentially affecting incident response capabilities.

Affected Products

Wireshark 4.6.0 to 4.6.4
Wireshark 4.4.0 to 4.4.14

Discovery Timeline

2026-04-30 - CVE CVE-2026-6521 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-6521

Vulnerability Analysis

This vulnerability exists within the OpenFlow v5 protocol dissector component of Wireshark. OpenFlow is a communications protocol that provides access to the forwarding plane of network switches and routers, commonly used in software-defined networking (SDN) environments. The dissector is responsible for parsing and displaying OpenFlow v5 protocol messages captured during network analysis.

The flaw manifests as an infinite loop condition (CWE-835) where the dissector fails to properly terminate when processing certain malformed OpenFlow v5 packets. When triggered, the application enters a state where it continuously processes without reaching an exit condition, effectively freezing the Wireshark interface and consuming CPU resources until the process is forcibly terminated.

The local attack vector requires user interaction, meaning an attacker must convince a victim to open a malicious capture file or analyze live traffic containing the specially crafted OpenFlow v5 packets. While this limits the attack surface, security analysts routinely analyze suspicious network captures, making them potential targets for this type of attack.

Root Cause

The root cause is an improper loop termination condition in the OpenFlow v5 protocol dissector. The dissector contains logic that fails to properly validate packet boundaries or field lengths, allowing malformed data to create conditions where the loop never satisfies its exit criteria. This results in an infinite loop that consumes CPU resources and renders the application unresponsive.

Attack Vector

The attack requires local access and user interaction. An attacker can exploit this vulnerability by:

Crafting a malicious PCAP file containing specially crafted OpenFlow v5 protocol packets designed to trigger the infinite loop condition
Distributing the malicious capture file through phishing, file sharing, or compromised network repositories
When a user opens the capture file in an affected version of Wireshark, the OpenFlow v5 dissector enters an infinite loop
The application becomes unresponsive, requiring forced termination and potentially losing unsaved analysis work

Alternatively, if an attacker can inject malformed OpenFlow v5 packets into network traffic being actively captured by a victim, the same denial of service condition can be triggered during live analysis.

For detailed technical information about the vulnerability, refer to the Wireshark Security Advisory WNPA-SEC-2026-39 and the related GitLab work items (#21182, #21188).

Detection Methods for CVE-2026-6521

Indicators of Compromise

Wireshark processes consuming 100% CPU with no apparent network traffic being processed
Wireshark application becoming unresponsive when opening specific capture files
Presence of suspicious PCAP or PCAPNG files containing OpenFlow v5 protocol data from untrusted sources
System resource exhaustion events correlated with Wireshark usage

Detection Strategies

Monitor for Wireshark processes that exhibit abnormal CPU consumption patterns without corresponding file I/O activity
Implement endpoint detection rules that flag Wireshark hangs occurring immediately after opening capture files
Use file analysis tools to pre-scan capture files for malformed OpenFlow v5 packets before opening in Wireshark
Deploy application whitelisting policies that alert on Wireshark process anomalies

Monitoring Recommendations

Configure process monitoring to alert when Wireshark processes exceed CPU usage thresholds for extended periods
Implement logging for capture file operations, including file source and hash values
Enable SentinelOne behavioral AI to detect application hang conditions and potential denial of service attacks
Monitor network analysis workstations for signs of resource exhaustion attacks

How to Mitigate CVE-2026-6521

Immediate Actions Required

Upgrade Wireshark to version 4.6.5 or later for the 4.6.x branch, or 4.4.15 or later for the 4.4.x branch
Avoid opening capture files from untrusted or unknown sources until patches are applied
Implement file quarantine procedures for capture files received via email or external transfers
Consider using alternative network analysis tools temporarily for analyzing captures from untrusted sources

Patch Information

Wireshark Foundation has addressed this vulnerability in updated releases. Users should consult the official Wireshark Security Advisory WNPA-SEC-2026-39 for detailed patch information. The patches correct the loop termination logic in the OpenFlow v5 protocol dissector to properly handle malformed packet data.

For tracking the specific code changes, refer to GitLab Work Item #21182 and GitLab Work Item #21188.

Workarounds

Disable the OpenFlow v5 dissector if not required for analysis work: Navigate to Analyze > Enabled Protocols and disable openflow_v5
Use TShark with specific dissector filters to exclude OpenFlow v5 processing when analyzing untrusted captures
Run Wireshark in a sandboxed environment or virtual machine when analyzing captures from untrusted sources
Implement process timeout mechanisms that automatically terminate Wireshark if it becomes unresponsive

bash

# Disable OpenFlow v5 dissector via command line
wireshark -o "openflow_v5.enabled:false" capture.pcap

# Use TShark with dissector disabled for batch processing
tshark -o "openflow_v5.enabled:false" -r capture.pcap

# Process capture with resource limits (Linux)
timeout 300 wireshark capture.pcap