UI Injection is a sophisticated attack technique where adversaries inject malicious code into the user interface layer of blockchain applications to create a divergence between what users see and what transactions actually execute on-chain. These attacks exploit the separation between the presentation layer (human-readable transaction details displayed in wallets or dApps) and the execution layer (actual bytecode and calldata sent to the blockchain).

The technique achieved widespread attention following the Bybit hack of February 2025, where attackers compromised the front-end interface of Bybit's Safe{Wallet} implementation. Through a supply chain attack that began with a malicious Docker container in the development pipeline, attackers eventually gained the ability to modify JavaScript code served from AWS S3 buckets. This allowed them to intercept and alter transaction data, displaying legitimate details to executives while substituting attacker-controlled addresses in the actual signed transactions, resulting in $1.5 billion in losses.

Attack Vectors and Technical Implementation

UI injection attacks can be implemented through multiple technical vectors depending on the target's infrastructure and security posture. Client-side injection modifies JavaScript code executed in users' browsers, typically by compromising the hosting infrastructure (AWS S3, CDN, or web servers) that serves the application's front-end assets. Once attackers can modify these assets, they inject code that intercepts transaction creation, alters parameters, and manipulates what users see on their screens.

DNS hijacking redirects users to attacker-controlled domains that perfectly replicate the legitimate interface while incorporating transaction manipulation code. Users believe they're interacting with the authentic application because the domain name appears correct in their browser, but every transaction they approve has been modified. This attack vector requires compromising DNS records or BGP routing, making it more difficult but enabling persistent access without touching the victim's actual infrastructure.

Man-in-the-middle (MITM) attacks at the network level can inject malicious code into HTTP responses before they reach users' browsers. While HTTPS/TLS prevents casual MITM attacks, sophisticated adversaries with network-level access (compromised routers, ISP-level access, or state-level actors) can potentially defeat TLS through certificate manipulation or protocol downgrade attacks. This makes HTTPS alone insufficient defense for high-security blockchain applications.

Browser extension compromise targets wallets and dApps implemented as browser extensions like MetaMask or browser-based interfaces. If attackers compromise the extension code through supply chain attacks on the development pipeline or malicious updates, they can inject transaction manipulation logic directly into the wallet interface. Users trust their wallet extension to display accurate transaction information, making this an extremely effective attack vector.

The Blind Signing Vulnerability

UI injection attacks specifically exploit the blind signing vulnerability—users' tendency to approve transactions based on interface displays without verifying underlying transaction data. Even sophisticated users with hardware wallets fall victim to these attacks because hardware wallet screens display simplified transaction summaries, not complete verification of all transaction parameters.

The Bybit incident demonstrated this perfectly. Executives used hardware wallets and followed organizational security procedures, yet still approved malicious transactions. The Safe{Wallet} interface displayed correct recipient addresses and amounts. The hardware wallet screens showed what appeared to be standard operations. Only by independently decoding the raw transaction hex—which none of the signers did—would they have discovered the manipulation.

This illustrates a fundamental limitation in current transaction signing workflows: the security model assumes users can effectively verify what they're signing, but the complexity of blockchain transactions and limitations of display technology make complete verification impractical for most operations. Attackers exploit this gap by compromising the trusted verification tools users rely on.

Prevention and Detection Strategies

Defending against UI injection requires defense-in-depth approaches that don't rely on any single point of trust. Subresource Integrity (SRI) provides cryptographic verification of front-end assets. By including integrity hashes in script tags (<script integrity="sha384-..." src="...">), browsers verify that loaded JavaScript files match expected hashes. This prevents attackers who compromise CDNs or caching infrastructure from serving modified code—browsers will refuse to execute scripts with incorrect hashes.

Content Security Policy (CSP) headers restrict what code can execute in the browser and where resources can be loaded from. A properly configured CSP prevents inline script execution, restricts script sources to specific trusted domains, and blocks eval and similar dynamic code execution mechanisms. This dramatically reduces the attack surface for code injection, though it requires careful configuration to avoid breaking legitimate application functionality.

Transaction simulation and verification provides runtime detection of manipulation. Before presenting transactions for signing, automatically simulate their execution in a separate environment and display the complete state changes they would produce. If the simulation reveals unexpected token transfers, permission changes, or contract interactions, flag the transaction as potentially malicious regardless of what the interface displays.

Operational Security for High-Value Operations

Organizations managing significant cryptocurrency holdings should implement independent transaction verification as mandatory procedure for all operations. This requires multiple signers to verify transaction details using completely separate tools and systems. One signer might verify using the primary interface, another using Etherscan's transaction decoder, and a third using command-line tools like Cast from Foundry. Only proceed if all verification methods show identical transaction details.

Air-gapped verification systems provide the highest level of assurance by performing transaction decoding and verification on systems physically isolated from potentially compromised networks. Generate transactions on networked systems, transfer raw transaction hex to an air-gapped computer via QR codes or USB, decode and verify on the isolated system, then return to the networked environment only for signature submission. This process is cumbersome but effectively eliminates network-based UI injection attacks.

Transaction signing policies should mandate waiting periods and multi-party verification for operations above certain value thresholds. A protocol might require that transactions moving more than $1 million wait 24 hours between proposal and execution, during which multiple independent parties review the transaction using different verification tools. This time delay creates detection windows that prevent attackers from immediately draining funds even if they successfully inject malicious transactions.

Developer Best Practices

Application developers building blockchain interfaces have responsibility to implement protections against UI injection attacks targeting their users. Deterministic transaction building on the backend rather than client-side reduces the attack surface. If transaction construction happens on trusted servers and clients only sign pre-built transactions, compromising client-side code provides less opportunity for manipulation. The trade-off is increased centralization and the need to trust backend infrastructure.

Transaction preview interfaces should display complete transaction details, not simplified summaries. Show full hex data, decoded contract calls with all parameters, and simulation results displaying exact state changes. While most users won't verify these details for routine operations, providing them enables power users and security researchers to detect manipulation attempts. The goal is making UI injection attacks detectable by someone, even if not all users verify every transaction.

Frontend integrity monitoring detects when deployed front-end code diverges from expected versions. Implement systems that regularly hash production front-end assets and compare against known-good versions. Alert when differences are detected, as this could indicate compromise. Some organizations publish hashes of their official front-end releases, allowing users to independently verify they're interacting with legitimate code.

Understanding UI injection attacks requires recognizing that in blockchain systems, the ultimate source of truth is not what appears on screens but what executes on-chain. Attackers who can manipulate the presentation layer while leaving the execution layer under their control can steal funds even from highly sophisticated users with hardware wallets and multi-signature security. Effective defense requires treating all user interfaces as potentially compromised and implementing independent verification through diverse tools and methods that don't share common points of failure.