What is CVE-2021-35300?

CVE-2021-35300 is a medium-severity vulnerability in Zammad, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 4.3/10. Published 2021-06-28.

How severe is CVE-2021-35300?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Zammad

CVE-2021-35300

Text injection/Content Spoofing in 404 page in Zammad 1.0.x up to 4.0.0 could allow remote attackers to manipulate users into visiting the attackers' page.

Published 2021-06-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (57.7th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 57.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Zammad

Weakness classification (CWE)

CWE-1021 — Improper Restriction of Rendered UI Layers or Frames (Clickjacking)

References

zammad.com/en/advisories/zaa-2021-07 (Patch, Vendor Advisory)

Frequently asked questions

What is CVE-2021-35300?: CVE-2021-35300 is a medium-severity vulnerability in Zammad, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 4.3/10. Published 2021-06-28.
How severe is CVE-2021-35300?: Medium severity. CVSS v3 base score is 4.3 out of 10.