Incident All ledgers

Poly Network: $611.0m

Poly Network lost $611.0m on 10 August 2021. Ranked 5th of 1,272 crypto failures, with method, returned funds and comparable incidents.

Date: 10 August 2021
Lost: $611.0m
Returned or repaid: None recorded
Target: DeFi Protocol
Category: Access Control
Method: Improper Access Control
Chains: Ethereum, BSC, Polygon

On August 10, 2021, an attacker exploited an access control and cryptography flaw in Poly Network's cross-chain bridge contracts, taking $611M across Ethereum, BSC and Polygon. Within 15 days the attacker voluntarily returned nearly all of it, keeping only transaction fees.

Against the ledger

It ranks 5th of the 1,272 incidents with a known loss, and 1st in 2021.
It accounts for 76.5% of the $798.2m in known losses in August 2021.
225 incidents in the ledger are classified as Access Control, for $1.96bn in total. This one is 31.1% of that.
The ledger records no returned funds.

Other incidents named Poly

Date	Target	Lost	Type	Method	Returned
02 Jul 2023	Poly Network	$5.0m	DeFi Protocol	Forged Proof	—

Closest in size by the same method

Date	Target	Lost	Type	Method	Returned
01 Apr 2026	Drift Trade	$295.0m	DeFi Protocol	Proxy Upgrade Hijack	—
12 Feb 2018	BitGrail	$170.0m	CEX	Improper Access Control	—
09 Nov 2017	Parity Multisig	$150.0m	DeFi Protocol	Uninitialized Proxy	—
08 Oct 2021	Mirror	$90.0m	DeFi Protocol	Improper Access Control	—
01 Apr 2025	UPCX	$70.0m	DeFi Protocol	Proxy Upgrade Hijack	—

On Bitminer.io

Poly Network Hack: Noble Mr. White Hat

All failures in 2021 · The failures ledger

Amounts are DefiLlama’s estimates and can change as incidents are revalued. Its returned figure can include money a company repaid itself, not only funds recovered from attackers. Source: DefiLlama.

Cite this Bitminer.io, “Poly Network, failures ledger”, data to 2 November 2026, https://bitminer.io/ledger/incident/poly-network-2021-08-10/. How this is built