CVE-2026-5407: Wireshark SMB2 DoS Vulnerability

CVE-2026-5407 Overview

CVE-2026-5407 is a denial of service vulnerability affecting Wireshark, the widely-used network protocol analyzer. The vulnerability exists in the SMB2 protocol dissector, where an infinite loop condition can be triggered when processing specially crafted network capture files or live traffic. This flaw (CWE-835: Loop with Unreachable Exit Condition) allows attackers to cause Wireshark to become unresponsive, consuming CPU resources indefinitely and disrupting network analysis operations.

Critical Impact
An attacker can cause denial of service by providing a maliciously crafted SMB2 packet capture, rendering Wireshark unusable for network troubleshooting and security analysis.

Affected Products

Wireshark 4.6.0 to 4.6.4
Wireshark 4.4.0 to 4.4.14

Discovery Timeline

2026-04-30 - CVE-2026-5407 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-5407

Vulnerability Analysis

This vulnerability is classified as CWE-835 (Loop with Unreachable Exit Condition), indicating a logic flaw in the SMB2 protocol dissector where certain input conditions cause the parsing loop to never terminate. When Wireshark processes maliciously crafted SMB2 protocol data, either from a capture file or live network traffic, the dissector enters an infinite loop that cannot be exited through normal execution paths.

The SMB2 (Server Message Block version 2) protocol is commonly used for file sharing in Windows environments. Wireshark's dissector for this protocol must parse complex nested structures and variable-length fields. The vulnerability likely resides in the handling of malformed length fields or recursive structure references that cause the parser to repeatedly process the same data without advancing.

The impact is a complete denial of service for the Wireshark application. Security analysts and network administrators relying on Wireshark for packet analysis will find the application frozen, requiring a forced termination. This is particularly concerning in incident response scenarios where real-time traffic analysis is critical.

Root Cause

The root cause is an infinite loop condition (CWE-835) in the SMB2 protocol dissector implementation. The loop fails to properly validate termination conditions when encountering malformed SMB2 packet structures. This allows specially crafted packets to cause the dissector to loop indefinitely without making progress through the data, resulting in application hang and CPU exhaustion.

Attack Vector

The attack requires local access and user interaction—an attacker must convince a victim to open a malicious packet capture file (.pcap, .pcapng) or capture live traffic containing the malicious SMB2 packets. Attack scenarios include:

Distributing malicious capture files through email attachments or file sharing platforms
Posting malicious captures on network analysis forums or educational resources
Compromising network infrastructure to inject malicious SMB2 packets into traffic being analyzed
Social engineering security analysts to examine "suspicious" traffic samples that contain the exploit

The vulnerability can be exploited without any prior authentication or special privileges on the target system.

Detection Methods for CVE-2026-5407

Indicators of Compromise

Wireshark process consuming 100% CPU on a single core for extended periods
Wireshark application becoming unresponsive when opening specific capture files or analyzing SMB2 traffic
Presence of unusually small or malformed .pcap or .pcapng files with SMB2 protocol data
User reports of application freezes specifically when filtering or dissecting SMB2 traffic

Detection Strategies

Monitor system processes for Wireshark instances exhibiting sustained high CPU utilization without corresponding network I/O activity
Implement file integrity monitoring on systems where capture files are stored to detect introduction of potentially malicious files
Use network monitoring tools to identify anomalous SMB2 traffic patterns that may indicate exploitation attempts
Deploy endpoint detection and response (EDR) solutions capable of identifying application hang conditions and potential DoS scenarios

Monitoring Recommendations

Configure process monitoring alerts for Wireshark instances that exceed CPU usage thresholds for extended durations
Implement logging for Wireshark crash events and forced terminations to track potential exploitation attempts
Monitor file system activity for suspicious capture file downloads or creations in common analysis directories
Establish baseline metrics for normal Wireshark resource consumption to identify anomalous behavior

How to Mitigate CVE-2026-5407

Immediate Actions Required

Update Wireshark to version 4.6.5 or later (for 4.6.x branch) or version 4.4.15 or later (for 4.4.x branch) immediately
Exercise caution when opening capture files from untrusted sources
Disable or limit SMB2 protocol dissection when analyzing untrusted traffic if updates cannot be applied immediately
Review recent capture files opened on affected systems to identify potential exploitation attempts

Patch Information

The Wireshark Foundation has addressed this vulnerability in their security advisory. Updated versions that remediate the infinite loop condition are available for download. Refer to the Wireshark Security Advisory WNPA-SEC-2026-11 for official patch information and download links. Additional technical details are available in the GitLab Wireshark Issue.

Workarounds

Avoid opening packet captures from untrusted or unknown sources until patched versions are deployed
Use alternative protocol analyzers (e.g., tshark with limited dissector options, tcpdump) for initial triage of untrusted captures
Configure Wireshark to disable the SMB2 dissector via Edit → Preferences → Protocols → SMB2 → Disable
Run Wireshark in sandboxed or isolated environments when analyzing potentially malicious traffic samples
Set resource limits on the Wireshark process to prevent complete system impact from infinite loop conditions

bash

# Disable SMB2 dissector via command line for tshark analysis
tshark -r suspicious_capture.pcap --disable-protocol smb2

# Alternative: Use tcpdump for initial inspection without SMB2 parsing
tcpdump -r suspicious_capture.pcap -n

# Resource limit configuration (Linux) to limit CPU impact
ulimit -t 300  # Set CPU time limit to 5 minutes before running Wireshark