CVE-2026-34063 affects Nimiq's network-libp2p implementation prior to version 1.3.0. The vulnerability occurs in the libp2p ConnectionHandler state machine which assumes at most one inbound and outbound discovery substream per connection. When a remote peer opens a discovery protocol substream a second time on the same connection, the handler triggers a panic condition instead of failing closed. This causes a remote crash of the networking task, taking the node's p2p networking offline until manual restart. The vulnerability allows remote attackers to cause denial of service by disrupting peer-to-peer networking functionality. A patch is available in version 1.3.0 with no known workarounds.