GEM · JULY 2026 · EARLY WARNING

Decidim HTML Content Blocks Vulnerability: Potential Script Execution

EARLY WARNING · UNCONFIRMED. This page describes a developing threat that 0Day surfaced from early signals and has not yet independently confirmed. Details may change. Always verify against the primary sources before acting.
GHSA-533C-2VH9-4R86Severity: HIGH

An early warning has been issued regarding a vulnerability in the Decidim gem that allows privileged admin users to store arbitrary HTML/JavaScript in HTML content blocks, which may execute in visitors' browsers.

What happened

The vulnerability, tracked as GHSA-533C-2VH9-4R86, affects various versions of the Decidim gem. It is reported that a privileged admin user can store arbitrary HTML/JavaScript in an HTML block on an affected landing page, which could execute in visitor's browsers. Exploitation of this vulnerability requires administrative access. It is recommended not to grant admin permissions to non-trustful users to mitigate potential risks.

Affected versions include multiple ranges from 0.14.0 to 0.32.0.rc3, with specific fixed versions noted for certain ranges. Users are advised to consult the primary sources for detailed version information and to apply necessary updates or patches as they become available.

This incident is currently under investigation, and further details may emerge. Users of the Decidim gem are encouraged to review their configurations and access controls to ensure they are not vulnerable to this potential attack vector.

How 0Day mitigates this

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