Security readout for executives and security teams
Plain-English summary
CVE-2020-36891 is a stored cross-site scripting issue in Kentico Xperience. An authenticated attacker could upload a file whose declared content type does not match its extension, causing script to run later in a user’s browser. Business risk is moderate, mainly affecting user trust, session safety, and content integrity.
Executive priority
Treat as a planned remediation item unless your Kentico site allows broad user uploads or supports sensitive administrative workflows. Prioritize faster if external users can upload content reviewed by staff or administrators.
Technical view
The issue is CWE-79 stored XSS in Kentico Xperience file upload handling. The source bundle identifies Kentico Xperience <= 12.0.49 as affected. CVSS 3.1 is 5.4: network exploitable, low complexity, low privileges required, user interaction required, scope changed, low confidentiality and integrity impact, no availability impact.
Likely exposure
Organizations running Kentico Xperience, especially version 12 installations at or below hotfix 12.0.49, should assess exposure. Risk is higher where lower-privileged users can upload files that other users or administrators later view.
Exploitation context
The attacker needs some authenticated upload capability and a victim must view the stored content. The source bundle does not show CISA KEV listing or cited evidence of active exploitation. This is not described as unauthenticated remote code execution.
Researcher notes
Evidence supports stored XSS through spoofed Content-Type during file upload. The bundle’s affected CPE data is sparse, but the advisory title identifies Xperience <= 12.0.49. No public exploit status or active exploitation evidence is provided in the supplied sources.
Mitigation direction
- Identify Kentico Xperience instances and their exact hotfix levels.
- Apply the relevant Kentico vendor hotfix or upgrade guidance.
- Restrict file upload permissions to trusted roles where possible.
- Enforce validation that file extensions and MIME types align.
- Review vendor guidance before relying on compensating controls.
Validation and detection
- Confirm whether any instance runs Kentico Xperience <= 12.0.49.
- Verify the applied Kentico hotfix level against the vendor hotfix page.
- Review upload workflows available to authenticated low-privilege users.
- Check logs or media libraries for suspicious mismatched uploaded files.
- Confirm browser-side script execution is blocked for uploaded content.
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 lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2020-36891 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
- Kentico DevNet HotfixesCVE reference · vendor-advisory, patch
- VulnCheck Advisory: Kentico Xperience <= 12.0.49 File Upload Stored XSSCVE reference · third-party-advisory
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.