DoS disclosure: Channel open race in CLN

Original Postby morehouse

Recent findings have highlighted a significant security risk within versions 23.02 to 23.05.2 of the C-Lightning (CLN) implementation, where nodes are exposed to a Denial of Service (DoS) attack through the exploitation of a race condition occurring during channel openings.

This vulnerability has been identified as a potential threat to user funds and stability of the network. Operators running any of these affected versions should immediately upgrade their systems to version 23.08 or later to mitigate this issue and safeguard their operations.

The core of the problem lies in a concurrency issue between the initiation of a channel opening and the establishment of a peer connection. In scenarios where these two processes intersect improperly, the software erroneously initiates the channeld daemon twice. This duplicate launch leads to an assertion failure, subsequently causing the node to crash. The severity of this flaw is underlined by the fact that an attacker can reliably induce such a crash within a mere 30 seconds by executing a specific fake channel DoS attack.

For node operators, the immediate course of action is to update to version 23.08, which contains necessary patches to prevent crashes resulting from this race condition. For those seeking an in-depth understanding of the vulnerability, its underlying causes, and methods for prevention, further details can be explored in an extensive discussion available on a dedicated blog post. It is crucial for participants in the network to stay informed and proactive in applying updates to ensure the integrity and continuity of the system.