Ontology halts mainnet block production over potential security concern

Ontology halted block production on its mainnet on August 31, 2026, as a preventive measure after developers flagged a potential security concern during a routine check. The freeze stopped at block 20,770,893, halting all on-chain transactions and bridge transfers. While Ontology reports no confirmed asset loss, South Korean exchanges Upbit and Bithumb suspended ONT, ONG, and MBL deposits and withdrawals. The incident occurs ten days after an upgrade to improve Ethereum compatibility.

Mainnet block production halt

• ▪Ontology stopped block production on its mainnet on August 31, 2026, freezing all on-chain transactions and bridge transfers
• ▪The last block produced on the Ontology mainnet before the suspension was block 20,770,893, recorded at 8:24:26 UTC on August 31, 2026

Potential security concern investigation

• ▪Ontology developers initiated the mainnet block-production halt as a preventive security measure after flagging a potential security concern during a routine daily check
• ▪Ontology reported that no security breach, active attack, or user asset loss had been confirmed based on its preliminary assessments during the mainnet pause

MainNet v3.1.2 upgrade timing

• ▪The MainNet v3.1.2 upgrade was designed to improve Ethereum compatibility by adding Ethereum Virtual Machine (EVM) opcodes to the Ontology network
• ▪The mainnet halt occurred approximately ten days after Ontology deployed its MainNet v3.1.2 upgrade around August 21, 2026

Network restart assessment process

• ▪Ontology has not established a specific timetable for resuming block production, stating that the pause will remain in place until a safety assessment is completed
• ▪Ontology announced that a separate update will be issued before or when block production restarts, following the completion of the technical review and any required upgrades

3 sources