CVE-2026-27153 in Discourse
Summary
by MITRE • 02/27/2026
Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, moderators could export user Chat DMs via the CSV export endpoint by exploiting an overly permissive allowlist in `can_export_entity?`. The method allowed moderators to export any entity not explicitly blocked instead of restricting to an explicit allowlist. Versions 2025.12.2, 2026.1.1, and 2026.2.0 patch the issue. No known workarounds are available.
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Analysis
by VulDB Data Team • 03/03/2026
The vulnerability identified as CVE-2026-27153 affects Discourse, an open source discussion platform that serves as a collaborative forum for communities and organizations. This security flaw resides in the permission model implementation within the platform's codebase, specifically impacting the CSV export functionality that moderators utilize to access user data. The issue represents a classic case of insecure direct object reference where access controls are improperly configured, allowing unauthorized data extraction through a misconfigured authorization mechanism.
The technical flaw manifests in the `can_export_entity?` method which implements an overly permissive allowlist approach rather than a restrictive denylist or explicit allowlist strategy. This method was designed to permit exports of specific entities while blocking others, but instead of maintaining an explicit whitelist of allowed export types, it relied on an implicit allowlist that permitted access to any entity not explicitly blacklisted. This design pattern creates a dangerous security boundary where the absence of explicit restrictions leads to unintended access privileges. The vulnerability falls under CWE-284 which categorizes improper access control issues, specifically addressing inadequate authorization checks in software applications.
The operational impact of this vulnerability is significant for organizations using Discourse as their primary communication platform, particularly those handling sensitive user data in private messaging contexts. Moderators with legitimate access rights could exploit this flaw to extract Chat DMs from any user within the system, potentially compromising user privacy and confidentiality. The ability to export user communications through the CSV endpoint creates a substantial risk for data leakage, especially in environments where user conversations contain personal information, proprietary data, or sensitive organizational discussions. This vulnerability directly impacts the principle of least privilege and could enable unauthorized data collection at scale.
The remediation for this vulnerability requires upgrading to Discourse versions 2025.12.2, 2026.1.1, or 2026.2.0, which implement proper access control measures through explicit whitelisting of exportable entities. Organizations should conduct immediate assessment of their Discourse installations to identify systems running vulnerable versions and implement the necessary upgrades as soon as possible. The lack of known workarounds means that administrators cannot patch the issue through configuration changes or temporary fixes, emphasizing the critical nature of applying the official security patches. This vulnerability also highlights the importance of following security best practices such as implementing principle of least privilege and conducting regular security assessments of access control mechanisms.
From an ATT&CK framework perspective, this vulnerability maps to technique T1078 which covers valid accounts and privilege escalation through the use of legitimate administrative credentials. The attack surface expands when considering T1567 which addresses data exfiltration through legitimate system access points. The vulnerability demonstrates how weak access control implementation can create persistent security risks that may go undetected for extended periods, potentially allowing attackers to establish long-term access to sensitive user communication data. Organizations should implement monitoring controls to detect unusual export activities and establish proper audit trails for administrative actions within their Discourse platforms to detect potential exploitation attempts.