Critical vulnerability in Zilliqa Ledger app exposes private keys

Zilliqa has disclosed a critical vulnerability in the official Ledger app that has been present in every release since 2019. Due to an error in nonce generation when signing native Zilliqa transactions, attackers can reconstruct a user’s private key from publicly available data on the blockchain. Accounts that have signed five or more native transactions via the Ledger app should be considered compromised.

zilliqa @zilliqa

Nonce-Generation Vulnerability in the Zilliqa Ledger App: A critical vulnerability has been identified in the Zilliqa Ledger application affecting the generation of Schnorr signatures for native (non-EVM) Zilliqa transactions. The vulnerability causes signatures to be generated with a predictably weakened ephemeral nonces, from which an attacker can recover the signer’s private key using only publicly available on-chain data.

Protective measures are already in place to prevent further loss, and a coordinated remediation plan is being finalised. Users who have signed native Zilliqa transactions with a Ledger device should await official guidance before taking any action.

Impact: The vulnerability affects private keys used to sign native Zilliqa transactions with a Ledger device. Any account that has broadcast approximately five or more native transactions signed through the Zilliqa Ledger app should be considered compromised. Its private key can be reconstructed from signatures already recorded on-chain, regardless of any subsequent software update.

The issue is confined to the Ledger app’s native signing path. EVM transactions are unaffected. Zilliqa software development kits, including zilliqa-js, gozilliqa-sdk and pyzil, generate nonces correctly and are not affected.

Root cause: Zilliqa native transactions are authenticated using EC-Schnorr signatures over secp256k1. Each signature requires a fresh, uniformly random 256-bit ephemeral nonce, (k). The secrecy and full-width randomness of (k) are essential, as any systematic bias can allow the private key to be recovered.

The signing routine generated 40 bytes of randomness and reduced them modulo the curve order, correctly producing a uniform 256-bit value. However, when copying this value into the nonce buffer, the code copied the wrong 32 bytes of the 40-byte output. This retained the eight zero-padding bytes introduced by the reduction and discarded eight bytes of entropy.

As a result, the most significant 64 bits of every generated nonce were fixed at zero, meaning (k < 2^{192}).

A nonce with 64 known bits leaks information about the private key with each signature. With five or more affected signatures, the private key can be recovered in seconds using commodity hardware by solving the resulting Hidden Number Problem through lattice reduction - a well-documented technique for attacking biased-nonce signatures.
Because the affected transactions are permanently recorded on-chain, this exposure cannot be reversed by updating the signing application. The affected keys must be retired.

Timeline
2019-2026: The defect was present in every released version of the Zilliqa Ledger app across all supported devices.

19 July 2026: On-chain activity consistent with active exploitation was observed.

21 July 2026: The root cause was isolated to the app’s nonce-handling code and confirmed by reproducing the issue against on-chain signatures.

Ongoing: A corrected version of the app is being prepared in coordination with Ledger. Release details will be announced separately.

Remediation: As soon as the issue was identified, native (non-EVM) transactions were suspended as a protective measure. This has halted further draining of affected accounts while a solution is prepared.

Affected accounts cannot be secured through an ordinary transfer. Because their private keys can be derived from data already recorded on-chain, an attacker with access to the same key could attempt to front-run a legitimate transfer as soon as transactions resume. Advising users simply to move their funds would therefore be ineffective and potentially unsafe.

A corrected build of the Ledger app has been prepared, restoring full-width nonce generation and preventing further weakened signatures from being produced. However, this does not protect keys that have already been used to sign affected transactions. Those keys must ultimately be retired.

A coordinated remediation plan to secure affected balances is being finalised and will be published separately. Until then, users who have signed native Zilliqa transactions with a Ledger device should take no independent action and should rely solely on official Zilliqa channels for instructions.

Users who hold or transact with ZIL exclusively through EVM-compatible tooling are not affected.

Acknowledgments: @kucoincom played a key role in pinpointing the root cause in the Zilliqa Ledger app nonce generation, recovered affected private keys from publicly available on-chain signatures, and confirmed ongoing exploitation.

KuCoin’s timely reporting and responsible collaboration enabled rapid protective measures, helping safeguard users, ecosystem participants, and the broader Zilliqa ecosystem while the remediation plan was being developed.

We sincerely appreciate the KuCoin team’s professionalism, technical expertise, and cooperation throughout this process.

22 Jul 2026View full tweet on X ›

How the vulnerability works

Native Zilliqa transactions use EC-Schnorr signatures over secp256k1. Each signature requires a random 256-bit nonce. In the Ledger app, the signing code generated 40 bytes of randomness, but when copying to the nonce buffer, the wrong 32 bytes were selected. As a result, eight bytes of zeros remained and eight bytes of entropy were lost. The consequence: the 64 most significant bits of every nonce were always zero.

With five or more signatures exhibiting this pattern, it is possible to recover the private key within seconds on ordinary hardware using so-called lattice reduction. Because the affected transactions are permanently on the blockchain, a software update does not resolve the issue for existing accounts. Those keys must be decommissioned.

On 19 July 2026, active exploitation was observed on the blockchain. Two days later, the cause was confirmed by reproducing the problem based on existing signatures. According to Zilliqa, KuCoin played a central role in identifying the cause, reconstructing affected private keys, and promptly reporting the active exploitation. Read more about hacks and exploits in the crypto world in our overview.

Suspended transactions and consequences for ZIL

As an immediate measure, Zilliqa has suspended all native transactions to limit further damage. EVM transactions are unaffected, as are the official software development kits such as zilliqa-js, gozilliqa-sdk and pyzil. Users who manage ZIL solely via EVM-compatible tools are not at risk.

The South Korean exchange Upbit reports Upbit that ZIL has been designated a warning asset on both the KRW and BTC markets. Deposits and withdrawals remain suspended, and the exchange states that it may terminate trading support if the issue is not resolved. Zilliqa urges users not to take independent action and to follow only the official channels for further instructions on securing affected funds.

Critical vulnerability in Zilliqa Ledger app exposes private keys

How the vulnerability works

Suspended transactions and consequences for ZIL

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