Polygon has pushed out two coordinated hard forks, Austin and Kyoto, to close security holes in its network. The upgrades, which were tested on the Amoy testnet before hitting mainnet, target denial-of-service, resource-exhaustion, and consensus-hardening risks. No mainnet disruption was observed from the vulnerabilities Austin addressed.
Why the Forks Were Issued
The forks were rolled out privately and validated on Amoy before activation. Austin, running on Bor v2.10.0, and Kyoto, on Heimdall v0.11.0, were both live on Amoy and mainnet by the time the disclosure went public. The vulnerabilities could have let attackers crash nodes or exhaust network resources, so the fixes were deployed without a public heads-up.
What Austin Changes
Austin adds an explicit per-block gas bound for state-sync events, which prevents denial-of-service attacks that might flood the chain with excessive sync data. It also removes Bor's TxDependency wire field, a feature that could cause crashes when handling arbitrarily large blobs. Both changes are designed to keep the network stable under hostile conditions.
Kyoto's Hardening Measures
Kyoto introduces a byte-level pre-scan for deeply nested google.protobuf.Any fields in Heimdall transactions, a safeguard against parsing attacks. Beyond that, it includes a batch of hardening fixes: a cap on fee-coin counts, normalized checkpoint signature recovery bytes, idempotent handling of repeated producer-downtime messages, milestone range votes bound to the signed parent hash, checkpoint-window continuity checks, non-halting future-span creation, and injective replay keys for topup, clerk, and stake L1 events. These changes tighten consensus logic and reduce the risk of chain splits or replay attacks.
Activation and Node Requirements
Austin activated at Amoy block 44,120,000 and mainnet block 91,949,700. Kyoto went live at Amoy height 42,252,000 and mainnet height 51,533,000. Both are binary upgrades, meaning no state migration or genesis change is required. Bor v2.10.0 is mandatory for all nodes, while Heimdall v0.11.0 is required for validators and full nodes. Nodes running pre-fork binaries past the activation heights have already forked off and need to upgrade and roll back to rejoin the network.
