Vulnerabilities in Multi-Signature Smart Contracts: How Attackers Bypassed Safe (Gnosis) Oracle Manipulation Checks in 2026

Executive Summary: In March 2026, a sophisticated attack vector emerged targeting multi-signature (multi-sig) smart contracts, specifically exploiting vulnerabilities in Safe (formerly Gnosis Safe), a leading Ethereum multi-sig wallet platform. Attackers leveraged adversary-in-the-middle (AiTM) techniques—similar to Evilginx-based MFA bypass methodologies documented in late 2024 and early 2025—to manipulate oracle data feeds and execute unauthorized transaction approvals. The incident highlights critical weaknesses in oracle integrity validation and the need for enhanced cryptographic and runtime monitoring defenses in decentralized governance systems.

Key Findings

• Exploitation of AiTM Techniques: Attackers used reverse proxy-based phishing (e.g., Evilginx variants) to intercept multi-factor authentication (MFA) sessions and session tokens, enabling unauthorized access to multi-sig signing interfaces.
• Oracle Manipulation via Data Feed Spoofing: By injecting falsified price or state data into trusted oracle networks (e.g., Chainlink, Pyth), attackers tricked multi-sig signers into approving transactions under false pretenses.
• Bypass of Safe’s Oracle Integrity Checks: Safe’s on-chain validation logic failed to detect discrepancies between signed transaction parameters and real-time oracle state, allowing malicious payloads to pass verification.
• Cross-Chain Impact: The attack vector extended beyond Ethereum, affecting Layer 2 rollups and sidechains relying on the same oracle infrastructure and multi-sig governance models.
• Low Detection Latency: Malicious transactions were confirmed within minutes due to delayed anomaly detection in oracle networks and governance UIs.

Detailed Analysis

1. Background: Multi-Sig and Oracle Dependencies

Multi-signature smart contracts require approval from multiple authorized parties before executing a transaction. These contracts often rely on external oracles to provide real-world data (e.g., asset prices, event outcomes) for conditional logic. Safe (Gnosis) is one of the most widely adopted multi-sig solutions, used by DAOs, institutional wallets, and DeFi protocols.

Oracles act as trusted data bridges between blockchains and off-chain systems. However, their integrity hinges on:

• Data authenticity (via cryptographic signatures)
• Consensus among multiple oracle nodes
• Real-time validation against on-chain state

When either component fails, the system becomes vulnerable to manipulation.

2. The Attack Chain: From MFA Bypass to Smart Contract Exploitation

The 2026 attack followed a multi-stage kill chain:

1. Initial Compromise via Evilginx-Style AiTM Phishing:
   • Victims received phishing emails or messages impersonating Safe’s interface or governance portals.
   • Links led to Evilginx reverse proxy servers mimicking legitimate login pages (e.g., safe.global).
   • Credentials and MFA tokens were captured via credential harvesting and session cookie theft.
2. Session Hijacking and Identity Spoofing:
   • Attackers used stolen session tokens to impersonate authorized signers within the Safe web interface.
   • Multi-sig sessions remained active due to long-lived JWTs or wallet connection persistence.
3. Oracle Manipulation and Payload Crafting:
   • Attackers identified a target transaction requiring oracle data (e.g., a price threshold for a swap).
   • Using a compromised node or Sybil attack on the oracle network, false price data was injected into the feed.
   • The manipulated value met the condition for execution (e.g., "price < threshold"), triggering a transaction proposal.
4. Bypassing Safe’s Oracle Checks:
   • Safe validates transaction parameters on-chain but does not re-verify oracle data at execution time.
   • It assumes oracle data is immutable once signed, but not all implementations enforce freshness or deviation checks.
   • The attacker’s falsified price was signed and accepted by the oracle network, passing Safe’s pre-flight checks.
5. Execution and Funds Drain:
   • Once enough signers (including the compromised account) approved, the transaction executed.
   • Funds were transferred to attacker-controlled addresses on Ethereum and other chains.

3. Technical Root Causes

The vulnerability stemmed from a combination of architectural and operational gaps:

• Inadequate Oracle Freshness Validation:

  Safe’s contracts did not enforce strict time-based validation of oracle data. Older, potentially stale prices could still trigger conditions.

• Lack of Runtime Anomaly Detection:

  While Safe performed transaction pre-checks, it lacked real-time monitoring for oracle deviation during the signing window.

• Over-Reliance on Off-Chain Trust:

  User interfaces and signing flows relied heavily on backend trust models, which were compromised via session hijacking.

• Ecosystem Fragmentation:

  Interoperability across oracle networks (Chainlink, Pyth, API3) created inconsistencies in data validation standards.

4. Comparison to Prior MFA Bypass Techniques

This incident is a logical evolution of AiTM attacks first documented in 2024–2025:

This progression shows a clear trend: attackers are escalating from credential theft to full transactional control by chaining social engineering with blockchain-level exploits.

Recommendations

For Multi-Sig Platforms (e.g., Safe)

• Implement real-time oracle freshness checks with configurable time windows (e.g., max 30-second delay).
• Introduce runtime anomaly detection in multi-sig contracts to flag transactions with oracle values deviating beyond statistical norms.
• Adopt hardware security modules (HSMs) or wallet signing devices that bind transactions to specific oracle states at signing