What is CVE-2021-27310?

CVE-2021-27310 is a medium-severity vulnerability in Csphere Clansphere, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-03-23.

How severe is CVE-2021-27310?

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

Is CVE-2021-27310 known to be exploited?

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

XSS in Csphere Clansphere

CVE-2021-27310

Clansphere CMS 2011.4 allows unauthenticated reflected XSS via "language" parameter.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-03-23 · 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: 0.028 (86.1th percentile), scored 2026-10-02.

Low probability of exploitation in the next 30 days, but still tracked. 86th percentile — 86.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.028 · newest: 0.028 · change: 0.000

Affected products

Csphere Clansphere — versions 2011.4

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

github.com/xoffense/POC/blob/main/Clansphere 2011.4 "language" xss.md (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-27310?: CVE-2021-27310 is a medium-severity vulnerability in Csphere Clansphere, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-03-23.
How severe is CVE-2021-27310?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-27310 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.