CVE-2026-76921 Overview
CVE-2026-76921 is a use-after-free vulnerability [CWE-416] in the Cryptographic Message Syntax (CMS) protocol dissector of Wireshark. The flaw affects Wireshark versions 4.6.0 through 4.6.7 and 4.4.0 through 4.4.18. An attacker can trigger a crash in the dissector by convincing a user to open a crafted capture file or by injecting malicious traffic onto a monitored network segment. Successful exploitation results in denial of service against the Wireshark process. The issue is tracked in Wireshark Security Advisory WNPA-SEC-2026-83.
Critical Impact
A malicious packet capture or crafted network traffic causes the Wireshark CMS dissector to crash, disrupting protocol analysis workflows and incident response investigations.
Affected Products
- Wireshark 4.6.0 through 4.6.7
- Wireshark 4.4.0 through 4.4.18
- Systems using affected Wireshark builds for live capture or offline analysis
Discovery Timeline
- 2026-08-19 - CVE-2026-76921 published to the National Vulnerability Database
- 2026-08-20 - Last updated in NVD database
Technical Details for CVE-2026-76921
Vulnerability Analysis
The vulnerability resides in the Wireshark CMS protocol dissector, which parses Cryptographic Message Syntax structures encountered in captured traffic. During dissection of malformed CMS data, the dissector references memory that has already been released, producing a use-after-free condition. The process crashes, terminating any active capture or ongoing analysis session.
Exploitation requires local user interaction. An analyst must open a crafted capture file, or the attacker must inject crafted packets onto a network segment where Wireshark performs live capture. The impact is limited to availability of the Wireshark process; the flaw does not permit code execution or data disclosure based on the published advisory.
Root Cause
The root cause is improper lifetime management of an object inside the CMS dissector code path. The dissector accesses a pointer after the underlying memory has been freed, matching the CWE-416 use-after-free pattern. Details of the offending function are tracked in GitLab Wireshark Work Item #21457 and GitLab Wireshark Work Item #21458.
Attack Vector
An attacker delivers a malicious .pcap or .pcapng capture file to an analyst, or transmits crafted CMS-bearing packets on a monitored network. When Wireshark parses the payload, the CMS dissector triggers the use-after-free and crashes. Because analysts frequently share capture files during incident response, phishing-style delivery is a plausible path. See the Wireshark Security Advisory WNPA-SEC-2026-83 for confirmed technical scope.
Detection Methods for CVE-2026-76921
Indicators of Compromise
- Repeated, unexpected crashes of the Wireshark process or tshark during CMS traffic analysis
- Capture files from untrusted sources containing malformed CMS structures
- Crash dumps referencing the CMS dissector or packet-cms.c code path
Detection Strategies
- Inventory installed Wireshark versions across analyst workstations and flag any build in the 4.6.0–4.6.7 or 4.4.0–4.4.18 ranges
- Monitor endpoint telemetry for abnormal termination of wireshark.exe, tshark, or dumpcap processes
- Scan shared capture repositories for files received from external parties before opening them in a vulnerable build
Monitoring Recommendations
- Alert on Wireshark process crashes correlated with the opening of externally sourced capture files
- Track software inventory changes to confirm patched versions are deployed across the fleet
- Log user activity involving capture-file downloads from email, chat, or ticketing systems
How to Mitigate CVE-2026-76921
Immediate Actions Required
- Upgrade Wireshark to a fixed release above 4.6.7 in the 4.6.x branch or above 4.4.18 in the 4.4.x branch as identified in WNPA-SEC-2026-83
- Restrict opening of capture files from untrusted or unverified sources on analyst workstations
- Communicate the risk to incident response teams that regularly exchange .pcap files
Patch Information
The Wireshark Foundation addressed the CMS dissector use-after-free in updates announced through Wireshark Security Advisory WNPA-SEC-2026-83. Apply the vendor-provided update package that matches the deployed branch. Corresponding fixes are tracked in GitLab Wireshark Work Item #21457 and GitLab Wireshark Work Item #21458.
Workarounds
- Disable the CMS protocol dissector in Wireshark preferences under Analyze → Enabled Protocols until the patch is installed
- Perform capture analysis of untrusted files inside an isolated virtual machine or sandbox
- Prefer command-line filtering with tshark disable options to avoid loading the CMS dissector when triage is required
# Disable the CMS dissector at runtime with tshark
tshark -r suspicious.pcapng --disable-protocol cms -Y "not cms"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
