What is CVE-2021-4124?

CVE-2021-4124 is a medium-severity vulnerability in Meetecho Janus, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-12-16.

How severe is CVE-2021-4124?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2021-4124 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Meetecho Janus

CVE-2021-4124

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

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-12-16 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (59.4th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 59.4% 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

Meetecho Janus
Meetecho Meetecho/janus-Gateway — versions unspecified

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

huntr.dev/bounties/a6ca142e-60aa-4d6f-b231-5d1bcd1b7190 (Exploit, Patch, Third Party Advisory)
github.com/meetecho/janus-gateway/commit/f62bba6513ec840761f2434b93168106c7c65a… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-4124?: CVE-2021-4124 is a medium-severity vulnerability in Meetecho Janus, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-12-16.
How severe is CVE-2021-4124?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-4124 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.