---
title: "CVE-2026-23891: Decidim has a cross-site scripting (XSS) in user name"
url: https://erroneo.us/security/cve/CVE-2026-23891/
description: "CVE-2026-23891 (decidim-core (RubyGems)): Decidim is a participatory democracy framework. In versions below 0.30.5 and 0.31.0.rc1 through 0.31.0, a stored…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-04-13
date_modified: 2026-05-13
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-23891"
kev: false
cvss: 9.3
epss: 0.00356
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-23891: Decidim has a cross-site scripting (XSS) in user name

**Signal:** Critical, preconditions apply. Severe if exploited, but exploitation needs conditions that may not apply to you. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4% , percentile 28: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 28% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes decidim-core (RubyGems) >= 0.31.0.rc1, < 0.31.0, fixed in 0.31.1 ; decidim-core (RubyGems) < 0.30.5, fixed in 0.30.5 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- RubyGems `decidim-core` >= 0.31.0.rc1, < 0.31.0 → fixed: 0.31.1
- RubyGems `decidim-core` < 0.30.5 → fixed: 0.30.5

## Affected products (CVE record)

- decidim decidim: >= 0.31.0.rc1, < 0.31.1, < 0.30.5

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.36% probability of exploitation activity in the next 30 days; percentile 28.

## Sources

- [GitHub Advisory GHSA-fc46-r95f-hq7g](https://github.com/advisories/GHSA-fc46-r95f-hq7g)
- [CVE.org record CVE-2026-23891](https://www.cve.org/CVERecord?id=CVE-2026-23891)
- [NVD entry CVE-2026-23891](https://nvd.nist.gov/vuln/detail/CVE-2026-23891)
- [github.com](https://github.com/decidim/decidim/security/advisories/GHSA-fc46-r95f-hq7g)
- [github.com](https://github.com/decidim/decidim/releases/tag/v0.30.5)
- [github.com](https://github.com/decidim/decidim/releases/tag/v0.31.1)
- [github.com](https://github.com/rubysec/ruby-advisory-db/blob/master/gems/decidim-core/CVE-2026-23891.yml)

---
Source page: https://erroneo.us/security/cve/CVE-2026-23891/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt