Security readout for executives and security teams
Plain-English summary
An authenticated user can place malicious script content into a new page description in flatCore-CMS 2.2.15. If another user views the affected content, the script may run in that user's browser. The CVE rates this as medium because it needs privileges and user interaction, but it can still affect confidentiality and integrity.
Executive priority
Treat as a moderate web application risk. Prioritize if flatCore-CMS is internet-facing, has many content editors, or supports privileged admin sessions in the same browser context.
Technical view
CVE-2021-40555 is a CWE-79 cross-site scripting issue in the new page creation description field of flatCore-CMS 2.2.15. The CVSS 3.1 vector is AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N, indicating network reachability, low complexity, required privileges, required victim interaction, changed scope, and no availability impact.
Likely exposure
Exposure is limited to organizations running flatCore-CMS 2.2.15 with users able to create pages. The source bundle does not identify other affected versions or CPEs.
Exploitation context
The source bundle does not show known active exploitation, and KEV is false. Practical risk depends on whether attackers can obtain low-privilege CMS access and entice a victim to view affected page content.
Researcher notes
Evidence is sparse: the CVE record names flatCore-CMS 2.2.15 and one GitHub issue, while affected vendor/product fields are listed as n/a. Do not assume broader version impact without vendor confirmation.
Mitigation direction
- Check flatCore-CMS vendor or issue tracker guidance for an official fix or workaround.
- Restrict page creation rights to trusted users until remediation is confirmed.
- Review existing page descriptions for unexpected script-like content.
- Apply output encoding or input sanitization if maintaining a private fork.
Validation and detection
- Confirm whether any deployed CMS instance is flatCore-CMS 2.2.15.
- Identify accounts or roles allowed to create new pages.
- Review description rendering for proper HTML output encoding.
- Check CMS content history for suspicious description edits.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-40555 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N2.32.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.4MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/flatCore/flatCore-CMS/issues/56CVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.