CVE-2021-40555Public exploitNetwork attack vector

Browser script execution via stored page description

Published Feb 16, 2023 · Updated Mar 19, 2025

Stored XSS in flatCore-CMS 2.2.15 allows remote authenticated users to run script in an administrator's browser via a page description. The page editor stores the description field without neutralizing active markup, and the all-pages admin view renders the stored value as executable content. Page creation or editing privileges are required; opening the page list triggers the payload in the viewer's session, enabling actions or data access available to that session.

CVSS severity5.4
Medium
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Stored XSS in flatCore-CMS 2.2.15 allows remote authenticated users to run script in an administrator's browser via a page description. The page editor stores the description field without neutralizing active markup, and the all-pages admin view renders the stored value as executable content. Page creation or editing privileges are required; opening the page list triggers the payload in the viewer's session, enabling actions or data access available to that session.

The record

CVE
CVE-2021-40555
Published
Feb 16, 2023
Updated
Mar 19, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 16, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 19, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.4CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo