What is CVE-2021-4020?

CVE-2021-4020 is a medium-severity vulnerability in Meetecho Janus, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-11-27.

How severe is CVE-2021-4020?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Meetecho Janus

CVE-2021-4020

janus-gateway is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-11-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.008 (56.4th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: +0.000

Affected products

Meetecho Janus
Meetecho Meetecho/janus-Gateway — versions unspecified

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

huntr.dev/bounties/9814baa8-7bdd-4e31-a132-d9d15653409e (Exploit, Patch, Third Party Advisory, Issue Tracking)
github.com/meetecho/janus-gateway/commit/d3fc00ec803d6c41d8f98908732f44e7f4911a… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-4020?: CVE-2021-4020 is a medium-severity vulnerability in Meetecho Janus, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-11-27.
How severe is CVE-2021-4020?: Medium severity. CVSS v3 base score is 5.4 out of 10.