TAC
EVM-compatible L2 associated with TON. The TON↔TAC bridge runs a lock-and-mint architecture and in May 2026 became the source of a $2.5M+ drain attack due to missing on-chain validator signature verification.
Aliases: tac chain, tac bridge, tac l2
TAC is an EVM-compatible L2 designed to extend TON toward the Ethereum ecosystem. The idea: let Solidity developers deploy on TON via a familiar EVM stack, and give TON users access to EVM liquidity through wrapped assets.
Architecture of the TAC ↔ TON bridge
The bridge uses the classic lock-and-mint pattern:
- Forward direction: a user locks a TON asset (USDT-jetton, TON, etc.) in the bridge-admin contract → TAC L2 validators sign the event → the wrapped asset is minted on TAC.
- Reverse direction: a user burns the wrapped asset on TAC → validators sign → bridge-admin on TON releases the original jetton.
Bridge vulnerability (May 2026)
On May 11, 2026 a drain attack started on the TAC bridge-admin contract. At the time of analysis, the attacker had stolen over $2.5M in wrapped jettons and 384K freshly-minted TAC. The root cause is architectural: bridge-admin contains zero CHKSIGN/CHKSIGNU/CHKSIGNS TVM instructions to verify TAC L2 validator signatures. Trust in Merkle roots is delegated to an off-chain rotator, which turns rotator compromise (or insider behaviour) into a one-step drain.
Full technical breakdown — see TAC Bridge Drain 2026: attack analysis. Using the TAC bridge before the patch with proper on-chain signature verification is not recommended.