CVE-2021-41082 in Discourse
Summary
by MITRE • 09/21/2021
Discourse is a platform for community discussion. In affected versions any private message that includes a group had its title and participating user exposed to users that do not have access to the private messages. However, access control for the private messages was not compromised as users were not able to view the posts in the leaked private message despite seeing it in their inbox. The problematic commit was reverted around 32 minutes after it was made. Users are encouraged to upgrade to the latest commit if they are running Discourse against the `tests-passed` branch.
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Analysis
by VulDB Data Team • 09/29/2021
CVE-2021-41082 represents a security vulnerability in the Discourse community discussion platform that exposed sensitive information through improper access control implementation. This vulnerability specifically affected private messages that contained group references, creating a data leakage scenario where unauthorized users could observe metadata about private communications. The flaw manifested as a disclosure of private message titles and participating user information to users who lacked proper authorization to access these messages. While the core access control mechanisms remained intact and users could not actually read the content of the private messages, the exposure of metadata created a significant privacy risk that violated fundamental security principles of information hiding and access isolation.
The technical implementation of this vulnerability stems from a problematic commit that introduced a flaw in the message visibility logic within Discourse's private messaging system. This issue falls under CWE-284 Access Control Flaw, specifically manifesting as improper access control where the system failed to properly enforce authorization checks for metadata exposure. The vulnerability existed for approximately 32 minutes before the problematic commit was reverted, providing a narrow window during which unauthorized users could potentially exploit this information disclosure. The affected system behavior demonstrates a failure in the principle of least privilege, where users received information beyond what they should have been authorized to access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it created potential for social engineering attacks and user privacy violations within community platforms. Attackers could potentially use the leaked metadata to identify users participating in private conversations, map community relationships, or infer sensitive information about group dynamics and user activities. This type of information leakage can be particularly damaging in environments where private discussions contain sensitive or confidential information. The vulnerability also demonstrates the importance of thorough testing and code review processes, as the issue remained undetected for a significant period despite being in a production branch.
Organizations running Discourse platforms should immediately upgrade to the latest commit available on the tests-passed branch to remediate this vulnerability. The recommended mitigation strategy includes verifying that all affected installations have been updated to the fixed version and conducting a security audit of private message communications to identify any potential exploitation attempts. System administrators should also review access logs for any unusual activity patterns that might indicate attempted exploitation of this vulnerability. The incident highlights the critical importance of maintaining up-to-date security practices and implementing proper change management procedures that include security validation before code deployment. This vulnerability aligns with ATT&CK technique T1211 Lateral Movement through information gathering, as unauthorized users could potentially use the exposed metadata to identify targets for further exploitation attempts.