What is CVE-2021-42567?

CVE-2021-42567 is a medium-severity vulnerability in Apereo Central Authentication Service, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-12-07.

How severe is CVE-2021-42567?

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

Is CVE-2021-42567 known to be exploited?

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

XSS in Apereo Central Authentication Service

CVE-2021-42567

Apereo CAS through 6.4.1 allows XSS via POST requests sent to the REST API endpoints.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-12-07 · 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: 0.081 (94.6th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 95th percentile — 94.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.081 · newest: 0.081 · change: 0.000

Affected products

Apereo Central Authentication Service

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

github.com/apereo/cas/releases (Third Party Advisory, Release Notes)
apereo.github.io/2021/10/18/restvuln/ (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-42567?: CVE-2021-42567 is a medium-severity vulnerability in Apereo Central Authentication Service, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-12-07.
How severe is CVE-2021-42567?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-42567 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.