How severe is CVE-2026-23891?

No CVSS score has been assigned to CVE-2026-23891 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-23891?

CVE-2026-23891 affects the following packages: decidim-core (RubyGems), decidim-core (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-23891?

Update decidim-core to 0.31.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23891 is resolved across your whole dependency graph.

How do I detect CVE-2026-23891 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for decidim-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-23891 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-23891 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-23891 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-23891?

CVE-2026-23891 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 30th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-23891?

CVE-2026-23891 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-23891 published, and has it been updated?

CVE-2026-23891 was published on April 13, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

Not in CISA KEV

CVE-2026-23891 — decidim-core

CVE-2026-23891 is a Cross-site Scripting (XSS) vulnerability in decidim-core. A fix is available for decidim-core — see the affected versions and patch details below.

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

Also known asGHSA-fc46-r95f-hq7g

Published

Apr 13, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23891.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs30th percentile — riskier than 30% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

💎decidim-core💎decidim-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

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).

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`decidim-core`	≥ 0.31.0.rc1&&< 0.31.1	0.31.1`bundle update decidim-core --conservative`
💎RubyGems	`decidim-core`	all versions	0.30.5`bundle update decidim-core --conservative`

Affected Products

1 product · 2 configurations

Application

decidimdecidim

≥ 0.31.0 && < 0.31.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for decidim-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update decidim-core to 0.31.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23891 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### 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](https://octree.ch/) and made by [Secu Labs](https://seculabs.ch/) against Decidim financed by the city of Lausanne (Switzerland).

O3 Security · Impact-Aware SCA

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CVE-2026-23891 — decidim-core

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

Real-World Exposure

Description

Impact

Patches

Workarounds

References

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2026-23891 in your dependencies?