The Cost of Ignoring the Constructor in a Proxy World

Proxies delegate calls to a mutable logic contract, but the proxy's own constructor runs only once. This creates a critical initialization gap where storage slots are uninitialized and ownership is unassigned, leaving $10B+ TVL across DeFi vulnerable to front-running and hijacking.\n- Initialization Race Conditions: Malicious actors can call initialize() before the legitimate deployer.\n- Uninitialized Storage: Logic contract assumptions about storage layout can be catastrophically wrong.

Protocols like OpenZeppelin enforce a canonical defense: separating construction from initialization and using a dedicated initializer function protected by an initializer modifier. This mimics constructor behavior in a proxy-safe way.\n- Access Control from Day Zero: The initializer function must atomically set the admin/owner.\n- Reentrancy Guard for Setup: Prevents re-initialization attacks that could reset permissions.

The EIP-1822 UUPS pattern moves upgrade logic into the implementation itself, not the proxy. This makes the constructor's role even more critical, as a flawed implementation deploy can permanently brick the proxy. The cost of error shifts from deployment gas to permanent immutability.\n- Implementation Self-Destruct Risk: A buggy implementation can remove its own upgrade function.\n- Gas Efficiency Trade-off: Saves ~30k gas per call but concentrates existential risk.

EIP-2535 Diamonds modularize logic into facets, each with its own constructor. This amplifies the problem: a system with 10+ facets has 10+ critical initialization points. A single missed init call can leave core functionality dead on arrival. The non-negotiable is a monolithic initialization script that atomically configures the entire diamond.\n- Orchestration Complexity: Initialization order and dependency management become paramount.\n- Storage Collision Guarantees: The diamond must enforce a clean storage layout across all facets from birth.

In 2017, a user accidentally triggered the kill() function in a library contract's constructor, permanently bricking ~587 wallets and freezing $160M+ in ETH. The flaw: the library was deployed as a standalone contract with an unprotected initialization function, not as part of a formal proxy pattern.\n- Root Cause: Misunderstood constructor behavior in delegatecall proxy architectures.\n- Lasting Impact: Cemented the need for explicit initializer modifiers and standardized upgrade patterns like Transparent & UUPS.

In 2022, an attacker exploited an uninitialized proxy in Audius's governance contract. The proxy's implementation had a constructor that set up critical storage variables, but this code is never run in a proxy context. The attacker called the initialization function themselves, granting themselves $1.1M in tokens.\n- Root Cause: Constructor logic not migrated to a separate initialize function.\n- Modern Lesson: UUPS proxies explicitly warn against constructor use, enforcing initialization via external function.

The industry's response standardized two defenses: the initializer modifier (OpenZeppelin) and UUPS proxies. Constructors are banned; all setup logic moves to a protected initialize() function.\n- Key Innovation: UUPS bakes upgrade logic into the implementation, making constructor vulnerabilities impossible.\n- Adoption Metric: $10B+ TVL now secured under these patterns, from Aave to Compound.

Deploying a proxy without initializing its implementation leaves storage slots wide open for hijacking. An attacker can become the owner before you do.

• Front-running Risk: Malicious actors can call initialize() before the legitimate deployer.
• Storage Collision: Poorly structured initialization can corrupt proxy storage, bricking the contract.
• Governance Capture: A single unguarded call can surrender control of $100M+ TVL protocols.

Relying on default OpenZeppelin TransparentUpgradeableProxy without a constructor is a silent risk. The admin slot is predictable and must be set atomically.

• Admin Slot 0: The proxy admin address is stored at a known storage slot; leaving it address(0) is catastrophic.
• No Atomic Deployment: Separate proxy and initialization transactions create a deadly race condition.
• Solution Pattern: Use a Proxy Factory or ProxyAdmin contract that deploys and initializes in one atomic transaction.

UUPS (EIP-1822) proxies bake upgrade logic into the implementation, not the proxy. A flawed constructor here dooms all future upgrades.

• Implementation Self-Destruct: If the implementation's constructor is upgradeable, a malicious upgrade can self-destruct the logic, freezing all assets.
• Initializer Access Control: The _disableInitializers() call in the implementation's constructor is non-negotiable for safety.
• Gas Efficiency Trade-off: Saves ~30k gas per call vs. Transparent proxies, but concentrates systemic risk.

The only safe pattern: make the implementation constructor trivial and non-upgradeable. All setup logic must move to a separate, protected initializer function.

• Constructor Best Practice: Only set immutable variables and call _disableInitializers() (for UUPS).
• Initializer Hardening: Use OpenZeppelin's Initializable with access control and reentrancy guards.
• Proven Tooling: Use Foundry's forge create with --constructor-args or Hardhat's deploy scripts to ensure atomicity.