Inside Qubic's Selfish Mining Campaign on Monero: Evidence, Tactics, and Limits

We analyze Qubic's publicly claimed selfish mining attack against Monero in 2025. By combining measurements from Monero nodes, the Qubic pool API, and Qubic-network observations, we reconstruct Qubic-attributed blocks and effective hashrate and identify ten intervals consistent with block withholding and strategic release. During these intervals, Qubic's average hashrate share rises to 23--34\%, yet we never observe sustained majority control. We evaluate the attack using the classical selfish mining model and a Markov-chain variant that captures Qubic's conservative release policy. At the inferred parameters, both models predict revenues below honest mining, and our measurements largely confirm this while showing systematic deviations. We attribute the gap to hashrate variability, coarse-grained interval detection, and operational frictions under community countermeasures. We further argue that selfish mining should be analyzed under time-varying hashrate. Even when the average hashrate stays below the static break-even point, an attacker can still run a profitable selfish-mining operation by operating it intermittently.