What is CVE-2021-42656?

CVE-2021-42656 is a medium-severity vulnerability in Sscms Siteserver Cms, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2022-05-24.

How severe is CVE-2021-42656?

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

XSS in Sscms Siteserver Cms

CVE-2021-42656

SiteServer CMS V6.15.51 is affected by a Cross Site Scripting (XSS) vulnerability.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2022-05-24 · 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: 0.007 (51.3th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 51st percentile — 51.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Sscms Siteserver Cms — versions 6.15.51

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/siteserver/cms (Third Party Advisory)
github.com/siteserver/cms/releases/download/siteserver-v6.15.51/siteserver_inst… (Patch, Third Party Advisory)
github.com/siteserver/cms/issues/3238 (Exploit, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-42656?: CVE-2021-42656 is a medium-severity vulnerability in Sscms Siteserver Cms, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2022-05-24.
How severe is CVE-2021-42656?: Medium severity. CVSS v3 base score is 5.4 out of 10.