Security readout for executives and security teams
Plain-English summary
This issue affects older Contao installations. Malicious content can be placed into the system log database table and then run in an administrator’s browser when the back-end system log is viewed.
Executive priority
Treat this as a targeted maintenance priority for affected Contao sites, not an emergency based on current evidence. Patch promptly where administrators use the back end, because browser execution in privileged sessions can support account or data compromise.
Technical view
CVE-2021-35210 is a cross-site scripting flaw in Contao 4.5.x through 4.9.x before 4.9.16 and 4.10.x through 4.11.x before 4.11.5. The source describes executable code injection into tl_log, triggered when the back-end system log is opened.
Likely exposure
Exposure is limited to Contao deployments running the affected version ranges, especially where administrators or privileged back-end users review system logs. The sources do not describe affected hosting models or required privileges for injecting tl_log content.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. Risk depends on whether an attacker can cause malicious content to enter tl_log and whether a back-end user views the system log.
Researcher notes
Key missing details include CVSS score, CWE assignment, injection preconditions, and proof of exploitation. The available description is clear on sink and trigger: tl_log content executes when the back-end system log is viewed.
Mitigation direction
- Upgrade Contao 4.5-4.9 deployments to 4.9.16 or later.
- Upgrade Contao 4.10-4.11 deployments to 4.11.5 or later.
- Check the Contao advisory and GitHub advisory for any environment-specific guidance.
- Restrict back-end access to trusted administrators until affected systems are updated.
Validation and detection
- Inventory Contao versions across production, staging, and legacy sites.
- Confirm no deployment runs Contao 4.5-4.9 before 4.9.16.
- Confirm no deployment runs Contao 4.10-4.11 before 4.11.5.
- Review system-log access patterns for unexpected administrative exposure.
- Check tl_log for suspicious HTML or script-like 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.
CVE-2021-35210 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://contao.org/en/security-advisories/cross-site-scripting-in-the-system-log-2021.htmlCVE reference · x_refsource_CONFIRM
- https://github.com/contao/contao/security/advisories/GHSA-h58v-c6rf-g9f7CVE reference · x_refsource_CONFIRM
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.