SlowMist traces Qubic wallet theft to weak randomness in seed generation

Blockchain security firm SlowMist has traced the theft of about 2.94 trillion QU from 1,404 Qubic wallets to weak randomness in the wallet’s seed generation, showing in a postmortem published October 20 that private keys could be recovered from as few as six network observations.

The attacker drained the wallets between 23:42 UTC on October 17 and 01:26 UTC on October 18, taking funds worth roughly $1.3 million to $1.4 million, Crowdfund Insider reported. Qubic’s validators, known as Computors, halted the network at tick 85,371,949 to stop further transfers.

Header values exposed the wallet’s random number stream

Qubic’s web wallet built each 55-letter account seed using JavaScript’s Math.random() function, without mixing in the user’s password, a device key or any other randomness source. While the seed format implies about 258 bits of strength, SlowMist said V8’s xorshift128+ generator allows at most 2^64 outcomes for a given call.

The same random stream also produced a “dejaVu” value written into Qubic’s network request headers, which the wallet’s bridge forwards to peers over plaintext TCP. SlowMist said six consecutive dejaVu values were enough to reconstruct the generator’s full 128-bit state in about 15 milliseconds in a local proof of concept, allowing an observer to predict seeds and verify them against public keys sent in balance requests.

Seeds created on iPhones and iPads in any browser, on Macs using Safari before October 18, or in the Qubic iOS app before July 2025 were affected. Qubic fixed seed generation in wallet version 4.26.4, which uses cryptographically secure randomness.

About 87.1% of the stolen QU remains frozen onchain, while the remaining 12.9% reached MEXC, which froze the receiving account about an hour after the deposit. Restitution will be decided by the Computor quorum, and Qubic has not announced a restart timeline.