CVE-2026-6533: Wireshark LZ77 DOS Vulnerability

CVE-2026-6533 Overview

A denial of service vulnerability exists in Wireshark's dissection engine related to LZ77 decompression handling. When processing specially crafted network capture files or live traffic, the application crashes due to improper control of a dropped element (CWE-1325). This vulnerability affects Wireshark versions 4.6.0 to 4.6.4 and 4.4.0 to 4.4.14, enabling attackers to disrupt network analysis operations.

Critical Impact
Attackers can cause Wireshark to crash by sending or providing malformed compressed data, disrupting network forensics and security monitoring activities.

Affected Products

Wireshark 4.6.0 to 4.6.4
Wireshark 4.4.0 to 4.4.14

Discovery Timeline

2026-04-30 - CVE-2026-6533 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-6533

Vulnerability Analysis

This vulnerability resides in Wireshark's LZ77 decompression routine within the dissection engine. The flaw relates to CWE-1325 (Improper Control of a Dropped Element), indicating that the decompression logic fails to properly handle certain element states during the decompression process.

When parsing network packets containing compressed payloads, the dissection engine performs LZ77 decompression to analyze protocol data. The vulnerability manifests when malformed or specially crafted compressed data triggers improper handling of dropped elements within the decompression state machine, leading to application crash.

This is a local attack vector requiring user interaction—the victim must open a malicious capture file or capture packets from a network where an attacker can inject crafted traffic. While no confidentiality or integrity impact exists, the availability impact is significant as Wireshark becomes unusable until restarted.

Root Cause

The root cause stems from improper control of dropped elements during LZ77 decompression (CWE-1325). The dissection engine's decompression routine fails to correctly manage element lifecycle states when processing certain boundary conditions in compressed data streams. This results in accessing or referencing elements that have been prematurely dropped or invalidated, causing memory access violations and subsequent application crashes.

Attack Vector

Exploitation requires local access and user interaction. An attacker can deliver a malicious packet capture file (.pcap, .pcapng) via email, web download, or file sharing. Alternatively, if the attacker has network access, they can inject malformed packets into traffic being monitored by Wireshark in live capture mode.

The attack sequence involves:

Crafting a packet capture containing malformed LZ77 compressed protocol data
Delivering the malicious capture file to a target analyst
The victim opens the file in Wireshark or captures live traffic containing the payload
Wireshark's dissection engine attempts to decompress the data
The decompression routine encounters the malformed element, triggering a crash

The vulnerability mechanism exists within the LZ77 decompression logic of Wireshark's dissection engine. When processing compressed protocol data, the decompression routine fails to properly validate and control element states, particularly when elements are dropped during the decompression process. This improper control leads to memory corruption and application crash. For detailed technical information, refer to the GitLab Issue #21127 and Wireshark Security Advisory 2026-28.

Detection Methods for CVE-2026-6533

Indicators of Compromise

Wireshark application crashes when opening specific capture files
Unexpected termination of wireshark or tshark processes during packet analysis
Error logs indicating segmentation faults or access violations in dissection engine components
Repeated Wireshark crashes when analyzing traffic from specific network segments

Detection Strategies

Monitor endpoint protection logs for repeated Wireshark process crashes or restarts
Implement file integrity monitoring on packet capture directories to identify potentially malicious files
Deploy SentinelOne agents to detect abnormal process termination patterns associated with Wireshark
Create correlation rules in SIEM to alert on multiple Wireshark crashes from the same workstation

Monitoring Recommendations

Enable crash reporting and core dump collection on analyst workstations running Wireshark
Monitor Windows Event Logs or system logs for application crash events related to Wireshark binaries
Implement behavioral analysis to detect unusual patterns of application crashes during network analysis activities
Review network traffic sources when crashes occur during live capture to identify potential malicious packet injection

How to Mitigate CVE-2026-6533

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 untrusted packet capture files until patches are applied
Use sandboxed environments or virtual machines for analyzing suspicious capture files
Consider temporarily disabling dissectors for protocols using LZ77 compression if feasible

Patch Information

The Wireshark Foundation has released security updates addressing this vulnerability. Users should upgrade to the latest stable release for their respective branches. Detailed patch information and fixed versions are available in the Wireshark Security Advisory 2026-28. The issue tracking and technical details can be found in the GitLab Issue #21127.

Workarounds

Analyze potentially malicious capture files using tshark with limited dissection scope to reduce attack surface
Use older capture file tools for initial triage before opening files in vulnerable Wireshark versions
Implement network segmentation to prevent malicious packet injection during live capture sessions
Configure file system permissions to restrict access to packet capture directories

bash

# Example: Disable specific protocol dissectors via command line
tshark -r suspicious.pcap --disable-protocol [protocol_name]

# Run Wireshark with limited dissection for initial analysis
wireshark -o "tcp.desegment_tcp_streams:FALSE" suspicious.pcap