Discourse is an open-source discussion platform. Prior to version 3.4.4 of the stable branch, version 3.5.0.beta5 of the beta branch, and version 3.5.0.beta6-dev of the tests-passed branch, sending a malicious URL in a PM to a bot user can cause a reduced the availability of a Discourse instance. This issue is patched in version 3.4.4 of the stable branch, version 3.5.0.beta5 of the beta branch, and version 3.5.0.beta6-dev of the tests-passed branch. No known workarounds are available.
The product does not properly control the allocation and maintenance of a limited resource.
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.