CVE-2026-40869

Not available

Workarounds

Disable amendment reactions for the amendable component (e.g. proposals).

The vulnerability allows any registered and authenticated user to accept or reject any amendments. The impact is on any users who have created proposals where the amendments feature is enabled. This also elevates the user accepting the amendment as the author of the original proposal as people amending proposals are provided coauthorship on the coauthorable resources.

The only check done when accepting or rejecting amendments is whether the amendment reactions are enabled for the component:
https://github.com/decidim/decidim/blob/9d6c3d2efe5a83bb02e095824ff5998d96a75eb7/decidim-core/app/permissions/decidim/permissions.rb#L107

The permission checks have been changed at 1b99136 which was introduced in released version 0.19.0. I have not investigated whether prior versions are also affected.

CVE-2026-40869 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.31.1, 0.30.5); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-40869? CVE-2026-40869 is a high-severity security vulnerability in decidim-core (rubygems), affecting versions >= 0.31.0.rc1, < 0.31.1. It is fixed in 0.31.1, 0.30.5.
2. How severe is CVE-2026-40869? CVE-2026-40869 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of decidim-core are affected by CVE-2026-40869? decidim-core (rubygems) versions >= 0.31.0.rc1, < 0.31.1 is affected.
4. Is there a fix for CVE-2026-40869? Yes. CVE-2026-40869 is fixed in 0.31.1, 0.30.5. Upgrade to this version or later.
5. Is CVE-2026-40869 exploitable, and should I be worried? Whether CVE-2026-40869 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-40869 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-40869?
   • Upgrade decidim-core to 0.31.1 or later
   • Upgrade decidim-core to 0.30.5 or later