On Sept. 8, 2025, SwissBorg suffered a major exploit resulting in the theft of 192,600 SOL tokens, worth $41.3M, across eight malicious transactions.

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SwissBorg, a leading European wealth app, offers an Earn product that enables users to deposit funds and earn yield through staking. To provide this service, SwissBorg relies on Kiln, a professional staking operator responsible to manage staking operations, deposits, and withdrawals.

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‍Kiln’s infrastructure was compromised prior to the attack. The attackers used their access to tamper with the payload of a legitimate unstake transaction.

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What should have been a routine operation was silently modified: the transaction now included extra instructions to reassign the Withdrawer Authority of multiple SwissBorg stake accounts to attacker-controlled addresses.

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This single injected change immediately handed full control of the wallets to the attacker. From that moment, neither SwissBorg nor Kiln could regain control of the affected funds.

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Understanding Solana Staking Authorities

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On Solana, each stake account has two distinct authorities:

• Staker Authority: decides which validator the tokens are delegated to.
  
  
• Withdrawer Authority: controls who can withdraw the funds.

By reassigning the Withdrawer Authority, the attacker effectively took ownership of the funds, gaining the ability to deactivate and fully withdraw the staked assets.

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The Attack Flow

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• Aug. 31, 2025 — Initial Compromise and Payload Injection:
  The attacker, having already breached Kiln’s infrastructure, modified a transaction intended to perform a standard unstake operation for SwissBorg. The injected payload included instructions to change the Withdrawer Authority to attacker-controlled addresses. (See the transaction here.)
  
  
• Sept. 8, 2025 — Funds Withdrawal:
  The attacker withdrew 192,600 SOL across eight transactions, stealing $41.3 million in total. (See the exploiter address here.)
  
  

Blind Signing

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While the original compromise of Kiln API enabled the attackers to provide a malicious payload, the attack could still be prevented if Swissborg were able to review the transaction prior to approving it for execution.

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This highlights a major vulnerability in transaction security - blind signing. Neither Kiln’s primary dashboard*, SwissBorg’s interface, nor the wallet software displayed the complete contents of the transaction or the hidden instructions, preventing the approvers from fully understanding and inspecting the impact of the transaction execution. 

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* It should be highlighted that Kiln provides a separate open-source decoding tool for avoiding blind signing transactions: https://sol.minitel.app/

How Hypernative Guardian Could Have Helped

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With Hypernative Guardian, this exploit could have been detected and stopped before any funds were lost. The Guardian provides full transaction visibility and security, including:

• Full Payload Inspection: Guardian inspects the entire transaction payload, not just the visible top-level action. It interprets all embedded instructions and parameters, including those added by a potentially compromised system or API.
• Transaction Simulation & Visibility: Before execution, Guardian simulates the transaction and provides human-readable visibility into what it will actually do onchain:
  
  • Which accounts will be modified;
  • Which authorities or balances will change;
  • What smart contract calls and functions are involved.
• Risk Detection: Guardian automatically identifies deviations from policy or unexpected actions, such as, in this case, the reassignment of Withdrawer Authority, which would be recognized as a high-severity risk.
• Real-Time Recommendation: Guardian generates a real-time recommendation on whether to proceed or deny. In this scenario, the transaction would have been flagged with a “Deny” recommendation and accompanied by a clear alert describing the unauthorized authority change.
• Automatic Denial: Guardian can be configured to automatically block or reject transactions that violate security policies. The manipulated unstake transaction would never have been executed or signed, effectively preventing the exploit altogether.

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The Core Lesson: Visibility Is Security

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The SwissBorg exploit wasn’t caused by smart contract logic, but constituted a failure of transaction visibility. A hidden instruction inside a legitimate-looking payload went unnoticed because no system verified what the transaction actually did.

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‍Hypernative Guardian solves this problem by bringing clarity and policy-based enforcement to every transaction. It ensures that no instruction is ever executed blindly, and that any anomaly, like an unauthorized authority change, is immediately detected and denied.

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Closing Thought

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The SwissBorg incident illustrates a growing challenge for all staking and custody platforms: complex, multi-instruction transactions are easy to abuse when their content isn’t fully transparent.

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With Hypernative Guardian, operators and services like SwissBorg can make every transaction verifiable, interpretable, and policy-enforced, ensuring that even if an attacker compromises part of the supply chain, the transaction itself cannot be weaponized.

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Hypernative Guardian brings the missing layer of trust through transparency, turning blind signing into secure signing.

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If your team is assessing its security posture, we’re here to answer questions and show how real-time protection can prevent the next incident. Reach out for a demo of Hypernative’s solutions, tune in to Hypernative’s blog and our social channels to keep up with the latest on cybersecurity in Web3.

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