The vulnerability is in Nimiq's network-libp2p implementation, where the ConnectionHandler state machine mistakenly assumes there can be at most one inbound and one outbound discovery substream per connection. If a remote peer initiates the discovery protocol substream twice over the same connection, the handler fails by triggering a panic in the code paths "Inbound already connected" or "Outbound already connected". This panic brings down the networking task (swarm) and renders the node's peer‑to‑peer network unusable until a restart. The weakness is an unchecked panic condition, identified as CWE‑617.

Nimiq network-libp2p versions before 1.3.0

The CVSS score of 7.5 indicates high severity. An attacker can trigger the flaw from any remote peer capable of establishing a connection to the node, making it readily exploitable in open or untrusted networks. EPSS score indicates a very low exploitation probability (<1%), and the vulnerability is not listed in CISA's KEV catalog. By forcing a node into an offline state, an adversary can achieve a denial‑of‑service effect until the node is manually restarted.