# Proxy & Upgradeability Security Audit

Systematic security audit for upgradeable smart contract patterns. Detects storage slot collisions, uninitialized implementation contracts, missing authorization, and upgrade mechanism vulnerabilities.

## Attack Patterns Covered

**1. Storage Slot Collisions (pre-ERC-1967)**
- Implementation slot at slot-0 collides with proxy admin storage
- Detection: check if impl uses `address public implementation` at slot 0
- ERC-1967 fix: `bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1)`

**2. Uninitialized Implementation (Parity $280M)**
- Unguarded `initialize()` on logic contract callable by anyone
- `selfdestruct` via delegatecall destroys proxy not impl
- Detection: verify impl has `_disableInitializers()` in constructor

**3. UUPS Missing Authorization (CVE-2021-32844)**
- `_authorizeUpgrade()` with empty body or missing `onlyOwner`
- Anyone can upgrade to malicious implementation
- Detection: grep `_authorizeUpgrade` for auth modifiers

**4. Storage Gap Corruption (Audius $6M)**
- Missing `__gap` array in base contract causes slot shift on upgrade
- New variable in base overwrites child contract storage
- Detection: verify `uint256[N] private __gap` present in all upgradeable base contracts

**5. Beacon Proxy Blast Radius**
- Single beacon key compromise upgrades ALL proxies simultaneously
- Detection: assess key management and upgrade timelock for beacon contracts

**6. Selector Clash (Transparent vs UUPS)**
- Function selector in implementation matches proxy admin function
- User calls routed to wrong target
- Detection: compare 4-byte selectors of impl public functions vs proxy functions

## Deliverables

- Line-by-line findings with severity (Critical/High/Medium/Low)
- Storage layout diff analysis across upgrade versions
- PoC demonstrating each exploitable pattern
- Recommended mitigations with code patches