CVE-2021-35955 json
Cross site scripting via HTML attributes in the back end
published 2021-08-12 5 y ago modified 2026-07-08 4 mo ago also GHSA-hr3h-x6gq-rqcp , EUVD-2021-1756
- cvss
- 4.8
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.6%
- EPSS 0.6% chance of exploitation in 30 days, percentile 46%
- public exploits
- 0
- none known
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.
Patch / fix
- packagist contao/core-bundle 4.4.56, 4.9.18, 4.11.7
- packagist contao/contao 4.4.56, 4.9.18, 4.11.7
- contao contao 4.4.56, 4.9.18, 4.11.7
Exploit prediction
0.56% chance of exploitation in the next 30 days, higher than 46% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| NVD | 3.1 | 4.8 | CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N |
| NVD | 2.0 | 3.5 | AV:N/AC:M/Au:S/C:N/I:P/A:N |
| GitHub | 3.1 | 5.9 | CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| packagist | contao/core-bundle | >=4.0.0, <4.4.56 >=4.5.0, <4.9.18 >=4.10.0, <4.11.7 |
4.4.56 4.9.18 4.11.7 |
| packagist | contao/contao | >=4.0.0, <4.4.56 >=4.5.0, <4.9.18 >=4.10.0, <4.11.7 |
4.4.56 4.9.18 4.11.7 |
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
contao.org
/en/news/contao-4-9-16-and-4-11-5-are-available.html
web, vendor-advisory
-
github.com
/contao/contao/security/advisories/GHSA-hr3h-x6gq-rqcp
web, third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2021-35955
advisory
-
contao.org
/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end.html
web
-
github.com
/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35955.yaml
web
-
github.com
/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35955.yaml
web
-
github.com
/contao/contao
package
Sources
- CVE List CVE-2021-35955
- GitHub Advisory GHSA-hr3h-x6gq-rqcp
- NVD CVE-2021-35955
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.