external-call-safety

Name: external-call-safety
Author: quillai-network

114stars23forks

How to install external-call-safety?

quillai-network/quillshield_skills/external-call-safety

$npx -y skills add quillai-network/quillshield_skills --skill external-call-safety

Installs into the current project.

Summary

Detects unsafe external call patterns and token integration vulnerabilities in smart contracts. Covers unchecked call/delegatecall/staticcall return values, fee-on-transfer tokens, rebasing tokens, tokens with missing return values (USDT), ERC-777 callback risks, unsafe approve r

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SKILL.md

1	# External Call Safety
2
3	Detect vulnerabilities arising from unsafe interactions with external contracts and non-standard token behaviors that break protocol assumptions. Covers OWASP SC06 (Unchecked External Calls) plus the entire "weird ERC20" problem space.
4
5	## When to Use
6
7	- Auditing any contract that calls external contracts (token transfers, cross-contract interactions)
8	- Reviewing protocols that support arbitrary/user-supplied ERC20 tokens
9	- Analyzing ETH payment distribution logic (airdrops, reward distribution, refunds)
10	- Verifying low-level call safety (`call`, `delegatecall`, `staticcall`)
11	- When a protocol claims to support "any ERC20 token"
12
13	## When NOT to Use
14
15	- Reentrancy-specific analysis (use reentrancy-pattern-analysis — though there is overlap)
16	- Oracle/price feed analysis (use oracle-flashloan-analysis)
17	- Pure access control review (use semantic-guard-analysis)
18
19	## Part 1: External Call Safety
20
21	### Vulnerability Class 1: Unchecked Return Values
22
23	Low-level calls (`call`, `delegatecall`, `staticcall`) return a boolean indicating success. If unchecked, failed calls are silently ignored.
24
25	```solidity
26	// VULNERABLE: Return value not checked
27	function withdraw(uint256 amount) external {
28	balances[msg.sender] -= amount;
29	payable(msg.sender).call{value: amount}(""); // Can fail silently!
30	// User's balance decreased but ETH not sent
31	}
32
33	// SAFE: Check return value
34	function withdraw(uint256 amount) external {
35	balances[msg.sender] -= amount;
36	(bool success, ) = payable(msg.sender).call{value: amount}("");
37	require(success, "Transfer failed");
38	}
39	```
40
41	Detection Algorithm:
42
43	```
44	For each low-level call expression:
45	1. Is the return value captured? (bool success, bytes memory data) = ...
46	2. Is the success boolean checked? require(success) or if(!success) revert
47	3. If not captured or not checked → UNCHECKED RETURN VALUE
48
49	Severity:
50	- ETH transfer unchecked → CRITICAL (funds lost)
51	- Token operation unchecked → HIGH (state desync)
52	- Non-financial call unchecked → MEDIUM
53	```
54
55	### Vulnerability Class 2: Gas Stipend Limitations
56
57	```solidity
58	// DANGEROUS: transfer() and send() forward only 2300 gas
59	payable(recipient).transfer(amount); // Reverts if recipient needs > 2300 gas
60	payable(recipient).send(amount); // Returns false, often unchecked
61
62	// SAFE: Use call() with gas
63	(bool success, ) = payable(recipient).call{value: amount}("");
64	require(success, "Transfer failed");
65	```
66
67	Why 2300 gas is dangerous:
68	- Contracts with `receive()` or `fallback()` that do more than emit an event will fail
69	- EIP-1884 changed `SLOAD` gas cost, breaking some existing contracts
70	- Multi-sig wallets and smart contract wallets often need more gas
71
72	### Vulnerability Class 3: Return Data Bomb
73
74	A malicious contract can return extremely large data to consume the caller's gas.
75
76	```solidity
77	// Vulnerable to return data bomb
78	(bool success, bytes memory data) = untrustedContract.call(calldata);
79	// If untrustedContract returns 1MB of data, copying it costs massive gas
80
81	// SAFE: Limit return data or ignore it
82	(bool success, ) = untrustedContract.call(calldata); // Ignore return data
83	// Or use assembly to limit return data size
84	```
85
86	### Vulnerability Class 4: Delegatecall to Untrusted Contract
87
88	```solidity
89	// CRITICAL: delegatecall executes untrusted code in OUR storage context
90	function execute(address target, bytes calldata data) external {
91	target.delegatecall(data); // Untrusted code can overwrite ANY storage
92	}
93
94	// delegatecall should ONLY be used with trusted, immutable targets
95	```
96
97	## Part 2: Token Integration Safety ("Weird ERC20" Tokens)
98
99	### Issue 1: Fee-on-Transfer Tokens
100
101	Some tokens deduct a fee during `transfer()` and `transferFrom()`. The recipient receives less than the specified amount.
102
103	```solidity
104	// VULNERABLE: Assumes received amount equals input amount
105	function deposit(uint256 amount) external {
106	token.transferFrom(msg.sender, address(this), amount);
107	balances[msg.sender] += amount; // Credits MORE than actually received!
108	}
109
110	// SAFE: Check actual balance change
111	function deposit(uint256 amount) external {
112	uint256 balanceBefore = token.balanceOf(address(this));
113	token.transferFrom(msg.sender, address(this), amount);
114	uint256 balanceAfter = token.balanceOf(address(this));
115	uint256 actualReceived = balanceAfter - balanceBefore;
116	balances[msg.sender] += actualReceived; // Credits actual amount
117	}
118	```
119
120	**

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external-call-safety

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View on GitHub

How to install external-call-safety?

quillai-network/quillshield_skills/external-call-safety

$npx -y skills add quillai-network/quillshield_skills --skill external-call-safety

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# External Call Safety
2
3	Detect vulnerabilities arising from unsafe interactions with external contracts and non-standard token behaviors that break protocol assumptions. Covers OWASP SC06 (Unchecked External Calls) plus the entire "weird ERC20" problem space.
4
5	## When to Use
6
7	- Auditing any contract that calls external contracts (token transfers, cross-contract interactions)
8	- Reviewing protocols that support arbitrary/user-supplied ERC20 tokens
9	- Analyzing ETH payment distribution logic (airdrops, reward distribution, refunds)
10	- Verifying low-level call safety (`call`, `delegatecall`, `staticcall`)
11	- When a protocol claims to support "any ERC20 token"
12
13	## When NOT to Use
14
15	- Reentrancy-specific analysis (use reentrancy-pattern-analysis — though there is overlap)
16	- Oracle/price feed analysis (use oracle-flashloan-analysis)
17	- Pure access control review (use semantic-guard-analysis)
18
19	## Part 1: External Call Safety
20
21	### Vulnerability Class 1: Unchecked Return Values
22
23	Low-level calls (`call`, `delegatecall`, `staticcall`) return a boolean indicating success. If unchecked, failed calls are silently ignored.
24
25	```solidity
26	// VULNERABLE: Return value not checked
27	function withdraw(uint256 amount) external {
28	balances[msg.sender] -= amount;
29	payable(msg.sender).call{value: amount}(""); // Can fail silently!
30	// User's balance decreased but ETH not sent
31	}
32
33	// SAFE: Check return value
34	function withdraw(uint256 amount) external {
35	balances[msg.sender] -= amount;
36	(bool success, ) = payable(msg.sender).call{value: amount}("");
37	require(success, "Transfer failed");
38	}
39	```
40
41	Detection Algorithm:
42
43	```
44	For each low-level call expression:
45	1. Is the return value captured? (bool success, bytes memory data) = ...
46	2. Is the success boolean checked? require(success) or if(!success) revert
47	3. If not captured or not checked → UNCHECKED RETURN VALUE
48
49	Severity:
50	- ETH transfer unchecked → CRITICAL (funds lost)
51	- Token operation unchecked → HIGH (state desync)
52	- Non-financial call unchecked → MEDIUM
53	```
54
55	### Vulnerability Class 2: Gas Stipend Limitations
56
57	```solidity
58	// DANGEROUS: transfer() and send() forward only 2300 gas
59	payable(recipient).transfer(amount); // Reverts if recipient needs > 2300 gas
60	payable(recipient).send(amount); // Returns false, often unchecked
61
62	// SAFE: Use call() with gas
63	(bool success, ) = payable(recipient).call{value: amount}("");
64	require(success, "Transfer failed");
65	```
66
67	Why 2300 gas is dangerous:
68	- Contracts with `receive()` or `fallback()` that do more than emit an event will fail
69	- EIP-1884 changed `SLOAD` gas cost, breaking some existing contracts
70	- Multi-sig wallets and smart contract wallets often need more gas
71
72	### Vulnerability Class 3: Return Data Bomb
73
74	A malicious contract can return extremely large data to consume the caller's gas.
75
76	```solidity
77	// Vulnerable to return data bomb
78	(bool success, bytes memory data) = untrustedContract.call(calldata);
79	// If untrustedContract returns 1MB of data, copying it costs massive gas
80
81	// SAFE: Limit return data or ignore it
82	(bool success, ) = untrustedContract.call(calldata); // Ignore return data
83	// Or use assembly to limit return data size
84	```
85
86	### Vulnerability Class 4: Delegatecall to Untrusted Contract
87
88	```solidity
89	// CRITICAL: delegatecall executes untrusted code in OUR storage context
90	function execute(address target, bytes calldata data) external {
91	target.delegatecall(data); // Untrusted code can overwrite ANY storage
92	}
93
94	// delegatecall should ONLY be used with trusted, immutable targets
95	```
96
97	## Part 2: Token Integration Safety ("Weird ERC20" Tokens)
98
99	### Issue 1: Fee-on-Transfer Tokens
100
101	Some tokens deduct a fee during `transfer()` and `transferFrom()`. The recipient receives less than the specified amount.
102
103	```solidity
104	// VULNERABLE: Assumes received amount equals input amount
105	function deposit(uint256 amount) external {
106	token.transferFrom(msg.sender, address(this), amount);
107	balances[msg.sender] += amount; // Credits MORE than actually received!
108	}
109
110	// SAFE: Check actual balance change
111	function deposit(uint256 amount) external {
112	uint256 balanceBefore = token.balanceOf(address(this));
113	token.transferFrom(msg.sender, address(this), amount);
114	uint256 balanceAfter = token.balanceOf(address(this));
115	uint256 actualReceived = balanceAfter - balanceBefore;
116	balances[msg.sender] += actualReceived; // Credits actual amount
117	}
118	```
119
120	**

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