What is CVE-2021-42090?

CVE-2021-42090 is a critical-severity vulnerability in Zammad, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-10-07.

How severe is CVE-2021-42090?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Deserialization in Zammad

CVE-2021-42090

An issue was discovered in Zammad before 4.1.1. The Form functionality allows remote code execution because deserialization is mishandled.

Vulnerability class: Insecure Deserialization

Published 2021-10-07 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.023 (82.9th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 83rd percentile — 82.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.023 · newest: 0.023 · change: 0.000

Affected products

Zammad

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

zammad.com/en/advisories/zaa-2021-14 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-42090?: CVE-2021-42090 is a critical-severity vulnerability in Zammad, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-10-07.
How severe is CVE-2021-42090?: Critical severity. CVSS v3 base score is 9.8 out of 10.