CVE-2021-39921Network attack vector

Denial of service via Modbus dissector null dereference

Published Nov 19, 2021 · Updated Aug 4, 2024

NULL pointer dereference in the Wireshark Modbus dissector in versions 3.4.0 through 3.4.9 and 3.2.0 through 3.2.17 allows remote attackers to cause denial of service via malformed packets or crafted capture files. The dissector dereferences a null pointer while processing malicious Modbus data, terminating Wireshark. Exploitation requires packet injection or convincing a user to open a crafted trace; impact is limited to analyzer availability.

CVSS severity7.5
High
EPSS probability3.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

NULL pointer dereference in the Wireshark Modbus dissector in versions 3.4.0 through 3.4.9 and 3.2.0 through 3.2.17 allows remote attackers to cause denial of service via malformed packets or crafted capture files. The dissector dereferences a null pointer while processing malicious Modbus data, terminating Wireshark. Exploitation requires packet injection or convincing a user to open a crafted trace; impact is limited to analyzer availability.

The record

CVE
CVE-2021-39921
Published
Nov 19, 2021
Updated
Aug 4, 2024
Vendor
Wireshark Foundation
Product
Wireshark
Classifications
CWE-476, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>=3.2.0, <3.2.18
  2. Affected versionversion=>=3.4.0, <3.4.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Wireshark Foundation · Wiresharkversion=>=3.2.0, <3.2.18; version=>=3.4.0, <3.4.10

Published CVSS scores

5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5GitLab CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo