CVE-2021-39921 Null dereference in Wireshark

What is CVE-2021-39921?

CVE-2021-39921 is a high-severity vulnerability in Debian Debian Linux, published on 19 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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

Weakness: CWE-476

Which versions are affected by CVE-2021-39921?

It affects 3 products.

Products include Debian Debian Linux, Fedoraproject Fedora, Wireshark Wireshark.

How do I fix CVE-2021-39921?

Upgrade to a fixed version.

Is CVE-2021-39921 being exploited?

There is no known exploitation of CVE-2021-39921 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-7409, DEBIAN-CVE-2021-39921, GHSA-5rpm-jh2v-38p6, UBUNTU-CVE-2021-39921.