access-control

# Access Control Vulnerability Analysis **2025 Statistics**: Access Control is **#1 vulnerability class** with **$953.2M in losses**. --- ## Why Access Control Bugs Happen (Root Causes) Understanding root causes helps detect vulnerabilities more effectively. ### Root Cause 1: Intent-Implementation Gap Developer thinks "only admin can call this" but forgets to add modifier. ```solidity // Developer INTENDED: only admin // ACTUAL: anyone can call function setPrice(uint256 newPrice) external { price = newPrice; // @audit No modifier! } ``` **Detection**: Find external/public functions without modifiers, then verify intent. ### Root Cause 2: Visibility ≠ Permission `external`/`public` means "anyone can call" - not a permission system. ```solidity // Visibility is NOT access control function withdraw() public { // @audit public ≠ "user's own funds" // Without checks, ANYONE withdraws ANYONE's funds } ``` **Detection**: Every state-changing external/public function needs explicit permission checks. ### Root Cause 3: Undefined Trust Boundary Who is "admin"? What can they do? Often undocumented. ```solidity // VULNERABLE: Admin powers undefined function emergencyWithdraw() external onlyAdmin { // Can admin steal all user funds? // Is this documented? Intended? } ``` **Detection**: Map all admin powers. Flag undocumented capabilities as centralization risks. ### Root Cause 4: Broken Permission Hierarchy Admin can create admins → single key compromise = total system takeover. ```solidity // VULNERABLE: Flat admin hierarchy function addAdmin(address newAdmin) external onlyAdmin { admins[newAdmin] = true; // @audit Compromised admin adds attacker } ``` **Detection**: Trace role grant paths. Flag self-granting or circular hierarchies. --- ## The Permission Matrix (Core Artifact) Build this for every contract: | Contract | Function | Sensitivity | Required Role | Actual Check | Gap? | |----------|----------|-------------|---------------|--------------|------| | Vault | withdraw | CRITICAL | User (own funds) | None | **YES** | | Vault | setFee | HIGH | Admin | onlyOwner | No | | Vault | pause | HIGH | Guardian | onlyAdmin | **WRONG ROLE** | | Token | mint | CRITICAL | Minter | None | **YES** | ### Sensitivity Classification | Level | Examples | Impact if Missing | |-------|----------|-------------------| | **CRITICAL** | withdraw, transfer, mint, upgrade | Direct fund loss | | **HIGH** | pause, setFee, setOracle | Protocol malfunction | | **MEDIUM** | setParameter, whitelist | Degraded operation | | **LOW** | view, pure functions | Information leak | --- ## Detection Patterns ### Pattern 1: Missing Access Control **Root Cause**: Intent-Implementation Gap ```solidity // VULNERABLE: Anyone can call function setPrice(uint256 newPrice) external { price = newPrice; // @audit Anyone can manipulate price! } function withdrawAll() external { payable(msg.sender).transfer(address(this).balance); // @audit No modifier! } ``` **Search Queries**: ``` Grep("function.*external(?!.*view)(?!.*pure)", glob="**/*.sol") Grep("function.*public(?!.*view)(?!.*pure)", glob="**/*.sol") ``` **Verification Questions**: - Does this function modify state? - Is there a modifier or require statement? - What is the intended caller? ### Pattern 2: Privilege Escalation **Root Cause**: Broken Permission Hierarchy ```solidity // VULNERABLE: Admin can add arbitrary admins function addAdmin(address newAdmin) external { require(admins[msg.sender], "Not admin"); admins[newAdmin] = true; // @audit Compromised admin adds attacker } // VULNERABLE: Self-grant role function grantRole(bytes32 role, address account) public { _grantRole(role, account); // @audit No permission check! } ``` **Search Queries**: ``` Grep("grantRole|addAdmin|setAdmin", glob="**/*.sol") Grep("_setupRole|_grantRole", glob="**/*.sol") ``` **Verification Questions**: - Can a role grant itself or other roles? - Is there a role hierarchy (admin > moderator > user)? - What happens if the top role is compromised? ### Pattern 3: tx.origin Phishing **Root Cause**: Confusing transaction origin with message sender ```solidity // VULNERABLE: Phishing via malicious contract function withdraw() external { require(tx.origin == owner); // @audit Phishing target! // Attacker tricks owner to call malicious contract // Malicious contract calls this function // tx.origin is still owner! } ``` **Search Queries**: ``` Grep("tx\\.origin", glob="**/*.sol") ``` **Verification Questions**: - Is tx.origin used for authorization? - Can an attacker trick the owner into calling a malicious contract? ### Pattern 4: Incorrect Permission Logic (OR vs AND) **Root Cause**: Logic error in permission checks ```solidity // VULNERABLE: Should be AND, not OR function sensitiveAction() external { require(hasRole(ADMIN) || hasRole(GUARDIAN)); // @audit OR allows either // Should require BOTH roles for high-sensitivity actions } // Also check for inverted logic function withdraw() external { require(!blacklisted[msg.sender]); // What if blacklist is empty? } ``` **Search Queries**: ``` Grep("require.*\\|\\|", glob="**/*.sol") Grep("require.*&&", glob="**/*.sol") ``` **Verification Questions**: - Should this be AND or OR? - What is the minimum permission needed? - Can the condition be bypassed? ### Pattern 5: Missing Two-Step Transfer **Root Cause**: No confirmation for critical ownership changes ```solidity // VULNERABLE: Single transaction transfer function transferOwnership(address newOwner) external onlyOwner { owner = newOwner; // @audit Typo in address = permanent loss } // SECURE: Two-step pattern function transferOwnership(address newOwner) external onlyOwner { pendingOwner = newOwner; } function acceptOwnership() external { require(msg.sender == pendingOwner); owner = pendingOwner; } ``` **Search Queries**: ``` Grep("transferOwnership|changeOwner|setOwner", glob="**/*.sol") Grep("pendingOwner|acceptOwnership", glob="**/*.sol") ``` **Verification Questions**: - Is ownership transfer single-step or two-step? - What happens if wrong address is provided? - Is there a timelock for ownership changes? ### Pattern 6: Role Hierarchy Exploitation (OpenZeppelin) **Root Cause**: Misunderstanding of AccessControl patterns ```solidity // VULNERABLE: DEFAULT_ADMIN_ROLE can grant any role // If compromised, attacker controls everything contract Vault is AccessControl { bytes32 public constant ADMIN_ROLE = keccak256("ADMIN"); constructor() { _grantRole(DEFAULT_ADMIN_ROLE, msg.sender); _grantRole(ADMIN_ROLE, msg.sender); // @audit DEFAULT_ADMIN_ROLE can grant ADMIN_ROLE to anyone } } ``` **Search Queries**: ``` Grep("DEFAULT_ADMIN_ROLE|AccessControl", glob="**/*.sol") Grep("_setRoleAdmin|getRoleAdmin", glob="**/*.sol") ``` **Verification Questions**: - Who holds DEFAULT_ADMIN_ROLE? - Is there a two-step admin transfer? - Can admin roles be renounced? --- ## Line-by-Line Verification Checklist For each external/public function: - [ ] Does this function modify state? - [ ] Is there a modifier applied? - [ ] Does the modifier check the correct role? - [ ] Can the require/revert condition be bypassed? - [ ] Who is the intended caller? Is this documented? - [ ] What is the worst case if anyone can call this? --- ## Centralization Risk Assessment Document admin powers that can harm users: | Admin Power | Risk Level | Impact | |-------------|------------|--------| | Pause withdrawals | High | Users locked out | | Change fee to 100% | Critical | Rug pull | | Upgrade implementation | Critical | Arbitrary code execution | | Mint unlimited tokens | Critical | Inflation attack | | Whitelist addresses | Medium | Censorship | | Change oracle | Critical | Price manipulation | **Flag as finding if**: - Power is undocumented - No timelock protection - Single key (not multisig) --- ## Search Query Reference ``` # Find all entry points Grep("function.*external|function.*public", glob="**/*.sol") # Find modifiers Grep("modifier\\s+\\w+", glob="**/*.sol") Grep("onlyOwner|onlyAdmin|only\\w+", glob="**/*.sol") # Find role management Grep("grantRole|revokeRole|renounceRole", glob="**/*.sol") Grep("transferOwnership|acceptOwnership", glob="**/*.sol") # Find dangerous patterns Grep("tx\\.origin", glob="**/*.sol") Grep("selfdestruct|delegatecall", glob="**/*.sol") ``` --- ## Rationalization Table (Reject These Excuses) | Excuse | Reality | |--------|---------| | "It's an internal function" | Internal functions can be called via public entry points | | "Only admin can call this" | Admin keys get compromised; document the risk | | "This is by design" | Document it as centralization risk if undocumented | | "Low likelihood" | Access control bugs caused $953M in losses | | "I'll check later" | Check NOW or miss critical vulnerabilities | | "The modifier exists somewhere" | Verify it's actually applied to THIS function | | "Frontend prevents this" | On-chain must be secure standalone |