CVE-2026-23891 Decidim has a Cross-site scripting (XSS) vulnerability via user name field

Critical 9.3 Published 13 Apr 2026 Updated 14 Apr 2026

A stored XSS vulnerability in Decidim allows attackers to execute arbitrary code in the context of other users visiting comment pages.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2026-23891?

CVE-2026-23891 is a critical cross-site scripting vulnerability in decidim, published on 13 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official description

Decidim is a participatory democracy framework. In versions below 0.30.5 and 0.31.0.rc1 through 0.31.0, a stored code execution vulnerability in the user name field allows a low-privileged attacker to execute arbitrary code in the context of any user who passively visits a comment page, resulting in high confidentiality and integrity impact across security boundaries. This issue has been fixed in versions 0.30.5 and 0.31.1.

Weakness: CWE-79

Which versions are affected by CVE-2026-23891?

4 open source packages ship an affected version, including decidim-core. It affects 1 product.

Package	Affected	Fixed in
`decidim-core` RubyGems	All versions	`0.30.5`
`decidim-core` RubyGems	All versions	`0.30.5`
`decidim-core` RubyGems	From `0.31.0.rc1`	`0.31.1`
`decidim-core` RubyGems	From `0.31.0.rc1`	`0.31.1`

Products include Decidim Decidim.

How do I fix CVE-2026-23891?

Upgrade decidim-core to a fixed version for your release line: 0.30.5 or 0.31.1.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2026-23891 being exploited?

There is no known exploitation of CVE-2026-23891 in the wild and no public exploit code.

Sources

Also known as GHSA-fc46-r95f-hq7g.