Syscoin Bridge Mints 5B Tokens via Parsing Bug, Repeats 2022 Pattern

Published by James Harris on June 17, 2026June 17, 2026

An attacker exploited a parsing inconsistency in Syscoin’s cross-chain bridge on June 7, minting 5 billion SYS tokens out of thin air before returning them in full after an on-chain warning from the team. The bridge remains offline. The tokens have since been burned.

The mechanics are specific enough to matter beyond Syscoin. The project runs a dual-layer architecture connecting a Bitcoin-based UTXO chain to an Ethereum-compatible smart contract layer called NEVM. The bridge between them verified transaction proofs before moving tokens, but the attacker crafted a transaction with two asset commitments pointing at the same output: one referencing native SYS, one referencing a custom test token. Syscoin Core read it as the test token; the NEVM relay read it as native SYS and released 5 billion tokens from the vault. The attacker had tested the approach with a smaller probe transaction first, according to the team’s postmortem published June 15. This kind of cross-layer parsing ambiguity is a recurring failure mode in bridge design, and the validation flaw in the proof verification logic here follows a pattern seen repeatedly since the Ronin and Wormhole exploits of 2022.

The 5 billion minted tokens exceeded Syscoin’s legitimate circulating supply of roughly 891 million SYS by more than five times. At exploit time, those tokens were worth around $9 million.

That $9 million figure lands differently given where Syscoin sits today. CoinMarketCap lists SYS at approximately $0.0026 with a total market cap of $2.3 million, down over 91% in the past year. DeFiLlama data showed TVL had already dropped to effectively zero before the incident, with only 14 active addresses and 73 transactions recorded in the 24 hours prior. The attacker returned the full 5 billion tokens after the team made on-chain contact and threatened exchange escalation and legal action, but the episode illustrates how bridge infrastructure can remain live and exploitable long after the ecosystem around it has hollowed out. PeckShield data recorded 14 major bridge exploits draining a combined $340.7 million through June 1, 2026, with bridge-related losses representing the largest single category in May alone at $28.62 million. Projects with declining user activity and speculative token dynamics tend to deprioritize security reviews precisely when their attack surface is most exposed.

The Syscoin team has updated the relay to reject any burn transaction where asset commitments are duplicated or could resolve inconsistently across layers, with consensus-level fixes to Syscoin Core still in progress. Native SYS deposits at exchanges resumed on June 10, but cross-chain transfers through the bridge remain paused pending final review. No timeline for reopening has been confirmed.