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Decidim amendments can be accepted or rejected by anyone

High severity GitHub Reviewed Published Apr 13, 2026 in decidim/decidim • Updated Apr 15, 2026

Package

bundler decidim-core (RubyGems)

Affected versions

>= 0.31.0.rc1, < 0.31.1
>= 0.19.0, < 0.30.5

Patched versions

0.31.1
0.30.5

Description

Impact

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.

Patches

Not available

Workarounds

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

References

@andreslucena andreslucena published to decidim/decidim Apr 13, 2026
Published to the GitHub Advisory Database Apr 14, 2026
Reviewed Apr 14, 2026
Last updated Apr 15, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

Weaknesses

Incorrect Privilege Assignment

A product incorrectly assigns a privilege to a particular actor, creating an unintended sphere of control for that actor. Learn more on MITRE.

CVE ID

CVE-2026-40869

GHSA ID

GHSA-w5xj-99cg-rccm

Source code

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