What’s Vulnerable › Vulnerabilities

CVE-2021-35955

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-12 · updated 2026-06-17
• Weakness: CWE-79

Description

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.

Affected products

• contao: from 4.0.0 before 4.4.56; from 4.5.0 before 4.9.18; from 4.10.0 before 4.11.7 — fixed in 4.11.7, 4.4.56, 4.9.18

How to fix

Upgrade to a fixed version: contao 4.11.7, 4.4.56, 4.9.18. Check the vendor advisory for mitigations.

References

• https://contao.org/en/news/contao-4-9-16-and-4-11-5-are-available.html
• https://github.com/contao/contao/security/advisories/GHSA-hr3h-x6gq-rqcp
• https://contao.org/en/news/contao-4-9-16-and-4-11-5-are-available.html
• https://github.com/contao/contao/security/advisories/GHSA-hr3h-x6gq-rqcp

Get alerted when CVE-2021-35955 or the next vulnerability affects your stack