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.

// 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.

// 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.

// 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.

// 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:

Sensitivity Classification

Detection Patterns

Pattern 1: Missing Access Control

Root Cause: Intent-Implementation Gap

// 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

// 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

// 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

// 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

// 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

// 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:

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)