Security readout for executives and security teams
Plain-English summary
Concrete CMS through version 8.5.5 had a weakness in how it cleaned SVG files. A malicious SVG might bypass sanitization, creating risk wherever users can upload or manage SVG content. The public bundle does not provide CVSS scoring or confirmed impact details.
Executive priority
Treat this as a targeted CMS hygiene issue, not a confirmed emergency from the provided evidence. Prioritize internet-facing or user-upload-enabled Concrete CMS sites, then update according to vendor guidance.
Technical view
CVE-2021-40104 is described as an SVG sanitizer bypass in Concrete CMS through 8.5.5. The available sources identify the affected version range and reference a HackerOne report and Concrete CMS 8.5.6 release notes, but the bundle does not include detailed root cause, CVSS, CWE, or exploit mechanics.
Likely exposure
Exposure is most likely on Concrete CMS deployments at or below 8.5.5, especially where authenticated or public workflows allow SVG upload, editing, or file-manager use. The source bundle does not identify affected roles, permissions, or whether anonymous users can trigger it.
Exploitation context
The CVE is not listed as CISA KEV in the provided bundle, and no cited source here confirms active exploitation. A HackerOne report exists, but the bundle does not provide exploit status or reproducible technical details.
Researcher notes
The evidence is thin: no CVSS, CWE, exploit status, detailed affected CPEs, or technical write-up content is present in the bundle. Avoid assuming XSS, stored payload behavior, or authorization requirements without reading the referenced HackerOne and vendor notes.
Mitigation direction
- Inventory Concrete CMS instances and identify versions through 8.5.5.
- Review Concrete CMS 8.5.6 release notes and vendor guidance.
- Apply vendor-supported updates or fixes for affected deployments.
- Limit SVG upload/use until vendor guidance is applied, where operationally feasible.
Validation and detection
- Confirm deployed Concrete CMS version on each instance.
- Review file upload workflows that accept SVG files.
- Check whether untrusted users can upload or manage SVG content.
- Verify remediation against Concrete CMS vendor release guidance.
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-2021-40104 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/1102088CVE 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.