Decidim Flaw Allows Unauthorized Amendment Acceptance
The National Vulnerability Database has disclosed CVE-2026-40869, a high-severity vulnerability (CVSS 7.5) affecting Decidim, a participatory democracy framework. This flaw, present in versions 0.19.0 up to 0.30.5 and 0.31.1, enables any registered and authenticated user to accept or reject amendments to proposals. This isn’t just a nuisance; it fundamentally subverts the integrity of the participatory process.
The impact is direct and significant for users who have created proposals with the amendments feature enabled. An unauthorized user accepting an amendment is effectively elevated to a co-author of the original proposal, gaining undue influence and potentially altering the intent or direction of community initiatives. This undermines trust and the democratic process Decidim aims to facilitate.
Defenders using Decidim must prioritize patching to versions 0.30.5 or 0.31.1 immediately. If immediate patching isn’t feasible, the National Vulnerability Database suggests a workaround: disable amendment reactions for any amendable components, such as proposals. This will mitigate the risk by removing the vulnerable functionality, though it may impact legitimate collaborative features.
What This Means For You
- If your organization utilizes Decidim for participatory governance or community engagement, this vulnerability is critical. An attacker can hijack the amendment process, effectively co-opting proposals and eroding the legitimacy of your platform. Immediately patch Decidim to versions 0.30.5 or 0.31.1. If you can't, disable amendment reactions on all proposals to prevent unauthorized modifications and co-authorship.
Related ATT&CK Techniques
🛡️ Detection Rules
2 rules · 6 SIEM formats2 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
CVE-2026-40869 - Decidim Unauthorized Amendment Acceptance
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-40869 | Privilege Escalation | Decidim versions 0.19.0 up to (excluding) 0.30.5 and 0.31.1 |
| CVE-2026-40869 | Auth Bypass | Decidim: authenticated users can accept/reject any amendments |
| CVE-2026-40869 | Misconfiguration | Decidim: disable amendment reactions for amendable components (e.g., proposals) as a workaround |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | April 21, 2026 at 23:17 UTC |
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