Contao >=4.0.0 allows backend XSS via HTML attributes to an HTML field.
Priority LOW 23CWE-79Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- High
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub. Impact type from CWE-79.
Summary
Contao >=4.0.0 allows backend XSS via HTML attributes to an HTML field. Fixed in 4.4.56, 4.9.18, 4.11.7.
Why it matters now
EPSS 0.00557 46th percentileScored 2026-11-07
Fix Fixed contao/core-bundle (Packagist): 4.4.56, 4.9.18, 4.11.7contao/contao (Packagist): 4.4.56, 4.9.18, 4.11.7
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
| — | contao/core-bundle (Packagist) | 4.0.0 to before 4.4.56 | 4.4.56 | Patch available | GHSA-hr3h-x6gq-rqcp |
| — | contao/contao (Packagist) | 4.0.0 to before 4.4.56 | 4.4.56 | Patch available | GHSA-hr3h-x6gq-rqcp |
| — | contao/contao (Packagist) | 4.5.0 to before 4.9.18 | 4.9.18 | Patch available | GHSA-hr3h-x6gq-rqcp |
| — | contao/contao (Packagist) | 4.10.0 to before 4.11.7 | 4.11.7 | Patch available | GHSA-hr3h-x6gq-rqcp |
| — | contao/core-bundle (Packagist) | 4.5.0 to before 4.9.18 | 4.9.18 | Patch available | GHSA-hr3h-x6gq-rqcp |
| — | contao/core-bundle (Packagist) | 4.10.0 to before 4.11.7 | 4.11.7 | Patch available | GHSA-hr3h-x6gq-rqcp |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
- contao/core-bundle (Packagist) Vendor— Affected 4.0.0 to before 4.4.56 Fixed in 4.4.56 Patch available GHSA-hr3h-x6gq-rqcp
- contao/contao (Packagist) Vendor— Affected 4.0.0 to before 4.4.56 Fixed in 4.4.56 Patch available GHSA-hr3h-x6gq-rqcp
- contao/contao (Packagist) Vendor— Affected 4.5.0 to before 4.9.18 Fixed in 4.9.18 Patch available GHSA-hr3h-x6gq-rqcp
- contao/contao (Packagist) Vendor— Affected 4.10.0 to before 4.11.7 Fixed in 4.11.7 Patch available GHSA-hr3h-x6gq-rqcp
- contao/core-bundle (Packagist) Vendor— Affected 4.5.0 to before 4.9.18 Fixed in 4.9.18 Patch available GHSA-hr3h-x6gq-rqcp
- contao/core-bundle (Packagist) Vendor— Affected 4.10.0 to before 4.11.7 Fixed in 4.11.7 Patch available GHSA-hr3h-x6gq-rqcp
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:contao:contao:*:*:*:*:*:*:*:* | 4.0.0 to before 4.4.56; 4.5.0 to before 4.9.18; 4.10.0 to before 4.11.7 | Vulnerable | contao |
- cpe:2.3:a:contao:contao:*:*:*:*:*:*:*:* Versions 4.0.0 to before 4.4.56; 4.5.0 to before 4.9.18; 4.10.0 to before 4.11.7 Vulnerable ·contao
Remediation
- Fix · GHSA-hr3h-x6gq-rqcp contao/core-bundle (Packagist) Fixed in 4.4.56 Advisory →
- Fix · GHSA-hr3h-x6gq-rqcp contao/contao (Packagist) Fixed in 4.4.56 Advisory →
- Fix · GHSA-hr3h-x6gq-rqcp contao/contao (Packagist) Fixed in 4.9.18 Advisory →
- Fix · GHSA-hr3h-x6gq-rqcp contao/contao (Packagist) Fixed in 4.11.7 Advisory →
- Fix · GHSA-hr3h-x6gq-rqcp contao/core-bundle (Packagist) Fixed in 4.9.18 Advisory →
- Fix · GHSA-hr3h-x6gq-rqcp contao/core-bundle (Packagist) Fixed in 4.11.7 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2021-35955
- 2026-10-03 Alias added: GHSA-hr3h-x6gq-rqcp
References
Advisory 3
Other 4
- https://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end.html
- https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35955.yaml
- https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35955.yaml
- https://github.com/contao/contao
More Contao vulnerabilities
- TI-2022-09661 Contao Managed Edition v1.5.0 was discovered to contain a remote command execution (RCE)… CVSS 3.1CRITICAL 9.8
- TI-2024-30849 Unrestricted file upload in Contao CVSS 3.1MEDIUM 6.4
- TI-2023-18600 Contao cross site scripting vulnerability via input unit widget CVSS 3.1MEDIUM 6.5
- TI-2022-08709 Cross site scripting via canonical tag CVSS 3.1HIGH 7.2
- TI-2019-08602 Contao 4.x allows SQL Injection. CVSS 3.0CRITICAL 9.8
- TI-2024-30447 Remote command execution through file upload in contao/core-bundle CVSS 3.1HIGH 8.8
Sources
- CVE-2021-35955 · CVE Program
- CVE-2021-35955 · NVD
- FIRST EPSS
- GHSA-hr3h-x6gq-rqcp · GitHub Advisory Database · CC BY 4.0
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