A privileged admin user who can edit an affected landing page can store arbitrary HTML/JavaScript in an HTML block, and the public page renders it with html_safe and no output escaping.
This issue lets any admin who can edit an affected landing page store arbitrary HTML and JavaScript in an HTML block. The block is then rendered back through Decidim::ContentBlocks::HtmlCell#html_content without a sanitization boundary, so the script executes later in visitor's browsers.
<img width="1541" height="439" alt="decidim-html-xss-01" src="https://github.com/user-attachments/assets/acae1c06-8acb-49be-ab12-aabae33190ce" />
<img width="1540" height="752" alt="decidim-html-xss-02" src="https://github.com/user-attachments/assets/a2f1fa7f-03f3-4d17-b58b-f4db865443e9" />
See https://github.com/decidim/decidim/pull/16451
Do not give admin permissions to non-trustful users.
Stored XSS
This issue was discovered in a security audit organized by the Decidim Association and made by Radically Open Security against Decidim financed by NGI.
| Software | From | Fixed in |
|---|---|---|
decidim-core
|
- | 0.30.9 |
decidim-core
|
0.31.0.rc1 | 0.31.5 |
decidim-core
|
0.32.0.rc1 | 0.32.0 |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.