Security readout for executives and security teams
Plain-English summary
Concrete CMS sites through 8.5.5 can store malicious script content in Conversations when the editor is set to Rich Text. If viewed by another user, especially an administrator, this could lead to account-impacting browser actions. The source bundle does not provide CVSS, CWE, or detailed fix text.
Executive priority
Treat this as a near-term web application remediation item, not an emergency based on current evidence. Prioritize internet-facing or administrator-used Concrete CMS sites because stored XSS can convert low-privilege content access into higher-impact browser compromise.
Technical view
CVE-2021-40100 is a stored cross-site scripting issue in Concrete CMS Conversations tied to the Active Conversation Editor Rich Text setting. The affected range is described as Concrete CMS through 8.5.5. The public sources identify the vulnerability class and configuration condition but do not include exploit status or detailed remediation steps.
Likely exposure
Exposure is most likely on Concrete CMS deployments running 8.5.5 or earlier with Conversations enabled and Rich Text selected for the Active Conversation Editor.
Exploitation context
The source bundle does not show CISA KEV listing or cited active exploitation. A public HackerOne report exists, so technical details may be publicly discoverable, but exploitation should not be assumed from the provided evidence.
Researcher notes
Key gaps are missing CVSS, CWE, CPE, exploit maturity, and explicit patch wording in the provided bundle. Validation should focus on version, Conversations usage, Rich Text editor configuration, and vendor release guidance rather than assumptions about broader Concrete CMS exposure.
Mitigation direction
- Inventory Concrete CMS instances and identify versions through 8.5.5.
- Check Concrete CMS 8.5.6 release notes and current vendor guidance.
- Upgrade affected systems to a vendor-supported fixed release where applicable.
- Until remediated, restrict Rich Text Conversations to trusted users only.
- Review stored conversation content for unexpected script-like entries.
Validation and detection
- Confirm Concrete CMS version on every public and internal instance.
- Check whether Conversations are enabled on each instance.
- Verify Active Conversation Editor is not set to Rich Text on vulnerable versions.
- Review vendor release notes for the exact fixed version and upgrade path.
- After remediation, test conversation rendering for script execution prevention.
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-2021-40100 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/616770CVE 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.