Security readout for executives and security teams
Plain-English summary
Concrete CMS through 8.5.5 has a cross-site scripting issue tied to Markdown comments. A malicious comment could cause script execution in another user's browser if the vulnerable feature is present and reachable. The provided sources do not include CVSS, detailed scope, or confirmed exploitation.
Executive priority
Prioritize this for public Concrete CMS properties, especially sites allowing user comments. Business risk is mainly session theft, account abuse, reputational harm, or malicious content shown to visitors. Urgency is moderate because exploitation is not confirmed in the provided sources.
Technical view
CVE-2021-40105 describes XSS in Concrete CMS through 8.5.5 via Markdown Comments. The bundle does not specify authentication requirements, privileges needed, stored versus reflected behavior, or exact affected configurations. Concrete CMS 8.5.6 release notes are cited, but the provided text does not name a specific fix.
Likely exposure
Most likely exposure is internet-facing Concrete CMS sites at version 8.5.5 or earlier with Markdown comment functionality enabled or accessible. Exposure is lower where comments are disabled, restricted, or not using affected Concrete CMS versions.
Exploitation context
The source bundle does not show CISA KEV listing or any cited evidence of active exploitation. The issue is public and has a HackerOne report reference, so defenders should treat it as known but not confirmed exploited from these sources.
Researcher notes
Key missing details are CVSS, CWE mapping, authentication requirement, exploit prerequisites, and whether the XSS is stored. Avoid assuming broader Concrete CMS components are affected beyond Markdown Comments in versions through 8.5.5.
Mitigation direction
- Inventory Concrete CMS sites and identify versions through 8.5.5.
- Review Concrete CMS 8.5.6 release notes and vendor guidance for remediation.
- Upgrade or otherwise remediate affected deployments according to vendor instructions.
- Restrict or moderate comment features until remediation is confirmed.
- Monitor CMS admin and comment activity for suspicious script-like content.
Validation and detection
- Confirm the deployed Concrete CMS version on each public site.
- Determine whether Markdown comments are enabled or reachable.
- Review recent comments for unexpected script, HTML, or encoded markup.
- Check vendor release notes for the fixed version and applied update state.
- Verify no vulnerable version remains exposed after remediation.
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.
CVE-2021-40105 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
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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 and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://hackerone.com/reports/1102054CVE reference · x_refsource_MISC
- https://documentation.concretecms.org/developers/introduction/version-history/856-release-notesCVE reference · x_refsource_MISC
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.