Wanchain Cardano–BNB Chain Bridge — Non-injective signature encoding flaw (NIGHT)

Timeline: On July 20, 2026 between 14:46 and 14:55 UTC, an attacker drained 515.2 million NIGHT tokens from the Cardano-side treasury of Wanchain's Cardano-to-BNB Chain bridge in four rapid transactions over approximately 8-9 minutes. The primary exploit transaction (0a4861be5dd1cd0a5ccd7d38855ef8fe233563274c22c27adb4f5980535d2ea1, block 13702781) transferred 203,001,692.164714 NIGHT from the bridge lock address to attacker wallet W1. Three additional transactions transferred 129.6M, 120.4M and 62.1M NIGHT. Root cause (per BlockSec Phalcon, July 21): the bridge's TreasuryCheck Plutus V2 validator constructed signed messages by directly concatenating 14 variable-length redeemer fields without separators or length markers, allowing a legitimate BNB Chain signature authorizing ~3,110 NIGHT to be replayed on Cardano for a 203M NIGHT withdrawal — a ~65,000x amplification via field-boundary ambiguity. NIGHT price crashed 30-43% to a record low near $0.016. Wanchain took the bridge offline and began investigating. The Midnight Foundation issued clarifications on July 20 and 21 confirming the incident was isolated to the third-party Wanchain bridge infrastructure; the Midnight Network, validators, consensus and core infrastructure were fully secure. Approximately 90% of stolen NIGHT was aggressively liquidated via Cardano DEX swaps; W2 used 68.27M NIGHT as Liqwid collateral to borrow and extract ADA.