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GHSA-533c-2vh9-4r86

MediumCVSS 4.8 / 10
Published Jul 13, 2026·Last modified Jul 13, 2026
Affected Components(11)
RubyGems logodecidim-core
0.31.0.rc1
RubyGems logodecidim-core
0.31.3
RubyGems logodecidim-core
0.32.0.rc1
1 / 4
Description

Description

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.

Technical description

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" />

Impact

  • A user with landing-page editing rights for an affected scope can persist JavaScript that executes in visitor's browsers on that page.
  • Because exploitation already requires privileged administrative access, the practical risk is lower than a participant-controlled or unauthenticated stored XSS. It still creates a browser-execution primitive in a trusted admin-editable surface.

Patches

See https://github.com/decidim/decidim/pull/16451

Workarounds

Do not give admin permissions to non-trustful users.

Reference

Stored XSS

Credits

This issue was discovered in a security audit organized by the Decidim Association and made by Radically Open Security against Decidim financed by NGI.

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Risk Scores
Base Score
4.8

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.

Threat Intelligence
4.4

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.25%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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