CVE-2026-28282 in Discourse
Summary
by MITRE • 03/20/2026
Discourse is an open-source discussion platform. Versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 have a security flaw in the discourse-policy plugin which allowed a user with policy creation permission to gain membership access to any private/restricted groups. Once membership to a private/restricted group has been obtained, the user will be able to read private topics that only the group has access to. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, review all policies for the use of `add-users-to-group` and temporarily remove the attribute from the policy. Alternatively, disable the discourse-policy plugin by disabling the `policy_enabled` site setting.
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Analysis
by VulDB Data Team • 03/24/2026
The vulnerability described in CVE-2026-28282 affects the Discourse open-source discussion platform and specifically targets the discourse-policy plugin functionality. This security flaw represents a critical access control bypass that undermines the platform's group membership and content restriction mechanisms. The vulnerability exists in versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, where the policy plugin fails to properly validate group membership permissions, creating an avenue for unauthorized access to restricted content. The flaw directly impacts the platform's security model by allowing malicious actors with appropriate policy creation privileges to escalate their access rights beyond intended boundaries.
The technical implementation of this vulnerability stems from insufficient validation within the discourse-policy plugin's group membership handling logic. When users with policy creation permissions attempt to manipulate group access controls, the system fails to properly enforce authorization checks that should prevent arbitrary group membership assignment. This weakness creates a path where authenticated users can bypass normal group membership restrictions and gain access to private topics that should only be visible to legitimate group members. The vulnerability operates at the policy enforcement level, where the plugin's access control mechanisms are improperly configured to allow privilege escalation through policy manipulation.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential data leakage and information disclosure risks. Once a malicious user successfully exploits this flaw, they can access private topics and discussions that contain sensitive information, potentially including personal communications, internal discussions, or confidential organizational data. This access bypass affects the fundamental security model of Discourse's group-based access control system, where private groups serve as security boundaries for restricting content visibility. The vulnerability essentially undermines the platform's ability to maintain content confidentiality and enforce access restrictions that are critical for organizations relying on secure discussion platforms.
From a cybersecurity perspective, this vulnerability aligns with CWE-285 (Improper Authorization) and represents a privilege escalation flaw that enables unauthorized access to restricted resources. The ATT&CK framework categorizes this as a privilege escalation technique where an attacker with limited permissions can gain elevated access through manipulation of access control policies. Organizations using Discourse platforms face significant risk from this vulnerability, particularly those handling sensitive information or requiring strict access controls for different user groups. The vulnerability's exploitation requires only a user with policy creation permissions, making it accessible to insiders or attackers who have gained such privileges through other means.
The remediation approach for this vulnerability involves implementing the patched versions of Discourse that address the policy plugin's authorization logic. Organizations should immediately upgrade to versions 2026.3.0-latest.1, 2026.2.1, or 2026.1.2 where the vulnerability has been resolved. As a temporary workaround, administrators can review existing policies for the `add-users-to-group` attribute and remove it from any policies that should not permit arbitrary group membership assignment. This mitigation approach aligns with the principle of least privilege by limiting the scope of permissions available to policy creation users. Alternatively, organizations can disable the discourse-policy plugin entirely by setting the `policy_enabled` site setting to false, which provides a complete isolation of the vulnerable functionality until a proper upgrade can be implemented. The recommended approach should consider the organization's operational requirements and the criticality of the policy functionality in their specific deployment environment.