Security Digest · Vulnerability record
CVE-2026-23891: Decidim has a cross-site scripting (XSS) in user name
Decidim is a participatory democracy framework.
CVSS 9.3 Critical EPSS 0.4% · p28
Should you act?
Critical, preconditions apply
Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- 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.
From the GitHub advisory
Impact 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.
Patches N/A
Workarounds Not available
References OWASP ASVS v4.0.3-5.1.3
Credits This issue was discovered in a security audit organized by octree and made by Secu Labs against Decidim financed by the city of Lausanne (Switzerland).
Weakness type: CWE-79.
Product: decidim-core (RubyGems) · Assigned by: GitHub_M · Published: 2026-04-13
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| RubyGems | decidim-core | >= 0.31.0.rc1, < 0.31.0 | 0.31.1 |
| RubyGems | decidim-core | < 0.30.5 | 0.30.5 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| decidim | decidim | >= 0.31.0.rc1, < 0.31.1, < 0.30.5 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 4.0 | 9.3 Critical | 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 | 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 |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Attack requirements: none
- Privileges required: low (any account)
- User interaction: passive
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- 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.
Timeline
- — CVE record published by GitHub_M
- — GitHub-reviewed advisory GHSA-fc46-r95f-hq7g published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-fc46-r95f-hq7g github.com
- CVE.org record CVE-2026-23891 cve.org
- NVD entry CVE-2026-23891 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com