Discourse is an open-source discussion platform. Prior to versions 3.3.4 on the stable branch and 3.4.0.beta5 on the beta branch, someone who is about to reach the limit of users in a group DM may send requests to add new users in parallel. The requests might all go through ignoring the limit due to a race condition. The patch in versions 3.3.4 and 3.4.0.beta5 uses the lock step in service to wrap part of the add_users_to_channel service inside a distributed lock/mutex in order to avoid the race condition.
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Discourse | Discourse | * | 3.3.3 (excluding) |
| Discourse | Discourse | * | 3.4.0 (excluding) |
| Discourse | Discourse | 3.4.0-beta1 (including) | 3.4.0-beta1 (including) |
| Discourse | Discourse | 3.4.0-beta2 (including) | 3.4.0-beta2 (including) |
| Discourse | Discourse | 3.4.0-beta3 (including) | 3.4.0-beta3 (including) |
| Discourse | Discourse | 3.4.0-beta4 (including) | 3.4.0-beta4 (including) |
A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.