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CVE-2021-42567 Apereo Central Authentication Service

Affected softwareApereo Central Authentication Service
Severity6.1 Medium CVSS 3.1 2 scores
Fixed in6.4.2
WeaknessCross-site scripting (CWE-79)
Published7 Dec 2021
Updated17 Jun 2026

Description

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

Exploitation status

Exploited

Real-world exploitation reported by VulnCheck KEV. CISA has not confirmed it.

  • CISA KEV not listed
  • VulnCheck KEV listed Exploitation reported in the wild. Honeypot sightings · earliest 2024-01-22.
  • CISA Vulnrichment no assessment published
  • Indexed PoC 1 indexed Published artifacts you can open, in Nuclei.
  • EPSS 8.2% chance in 30 days

VulnCheck KEV

Exploitation evidence from VulnCheck Known Exploited Vulnerabilities (VulnCheck KEV), used under VulnCheck's community terms. View CVE-2021-42567 in VulnCheck (free account).

EvidenceSourceDetailDate
Honeypot sighting Shadowserver honeypots Exploitation attempts seen on 336 days 2024-01-22 to 2026-11-04
IndexArtifactStarsFirst seen
Nuclei Apereo CAS Cross-Site Scripting

Waratek protection

Mitigation candidate

A kind of vulnerability Waratek's rules address, with exploit code published or exploitation reported. No rule exists and none is planned yet. The decision below says what we found to build a rule from.

  • Protection none
  • Action unverified
  • Review automated Inferred
  • Record active
Decided by The affected package being open source on Maven, so the fix can be read
Finding This CVE affects an open-source Java library published on Maven Central (Maven packages: org.apereo.cas:cas-server-core-web), so it is squarely in ARMR's territory and the source needed to understand the defect is public. That makes it a candidate for an ARMR patch rule. No rule exists and none is scheduled: the diff between the affected and fixed versions has not been read, and a closer look may find no hook point ARMR can act on.

CVSS

6.1 MEDIUM v3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

VersionScoreBandVectorAssignerType
CVSS 3.1 6.1 MEDIUM CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N NVD Primary published
CVSS 2.0 4.3 none AV:N/AC:M/Au:N/C:N/I:P/A:N NVD Primary

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev
PackageIntroducedFixedLast affected
org.apereo.cas:cas-server-core-web 0 6.4.2 unbounded

Products and versions

2 products, 3 version entries
SourceVendorProductSchemeAffected versions
nvd apereo central authentication service generic ≥ 6.3.0 and < 6.3.7.1 · ≥ 6.4.0 and < 6.4.2
osv org.apereo.cas cas-server-core-web generic < 6.4.2

References

URLTags
https://github.com/apereo/cas/commit/376bf087d6d4267f61fc9f8028aa0d1ef407c3f0 WEB
https://apereo.github.io/2021/10/18/restvuln WEB
https://github.com/apereo/cas PACKAGE
https://github.com/apereo/cas/releases WEB
https://apereo.github.io/2021/10/18/restvuln/ Patch, Third Party Advisory

Timeline

Published2021-12-07By the CVE Program.
VulnCheck KEV: earliest evidence2024-01-22Date of the oldest evidence of exploitation in VulnCheck KEV's record. VulnCheck does not publish the date it listed the CVE.
NVD record modified2026-06-17NVD's own last-modified date for this record.
VulnCheck KEV: latest evidence2026-11-04Date of the newest report, exploit reference or honeypot sighting in VulnCheck KEV's record.