input-arithmetic-safety

Name: input-arithmetic-safety
Author: quillai-network

114stars23forks

How to install input-arithmetic-safety?

quillai-network/quillshield_skills/input-arithmetic-safety

$npx -y skills add quillai-network/quillshield_skills --skill input-arithmetic-safety

Installs into the current project.

Summary

Detects input validation failures and arithmetic vulnerabilities in smart contracts. Covers missing zero-address and zero-amount checks, division-before-multiplication precision loss, rounding direction exploitation, ERC4626 vault share inflation attacks, unsafe integer casting,

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SKILL.md

1	# Input & Arithmetic Safety
2
3	Detect input validation failures (the #1 direct exploitation cause at 34.6% of all contract exploits) and arithmetic vulnerabilities that persist even with Solidity 0.8+ checked math — precision loss, rounding exploitation, unsafe casting, and share price manipulation.
4
5	## When to Use
6
7	- Auditing any contract with public/external functions accepting user-supplied parameters
8	- Reviewing DeFi protocols with fee calculations, share pricing, or exchange rates
9	- Analyzing vault/staking contracts for rounding or first-depositor attacks
10	- Checking contracts with `unchecked` blocks for overflow/underflow risks
11	- Verifying arithmetic in token minting, burning, and distribution logic
12
13	## When NOT to Use
14
15	- Access control analysis (use semantic-guard-analysis)
16	- Reentrancy detection (use reentrancy-pattern-analysis)
17	- Full multi-dimensional audit (use behavioral-state-analysis)
18
19	## Part 1: Input Validation Analysis
20
21	### Critical Missing Validations
22
23	Zero Address Check:
24
25	```solidity
26	// VULNERABLE: No zero address check
27	function setAdmin(address newAdmin) external onlyOwner {
28	admin = newAdmin; // Can set admin to address(0) — locking out admin forever
29	}
30
31	// SAFE
32	function setAdmin(address newAdmin) external onlyOwner {
33	require(newAdmin != address(0), "Zero address");
34	admin = newAdmin;
35	}
36	```
37
38	Zero Amount Check:
39
40	```solidity
41	// VULNERABLE: Allows zero-amount operations
42	function deposit(uint256 amount) external {
43	balances[msg.sender] += amount;
44	emit Deposit(msg.sender, amount);
45	// Zero deposit: wastes gas, pollutes events, may affect accounting
46	}
47
48	// SAFE
49	function deposit(uint256 amount) external {
50	require(amount > 0, "Zero amount");
51	balances[msg.sender] += amount;
52	}
53	```
54
55	Array Length Validation:
56
57	```solidity
58	// VULNERABLE: No length check
59	function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
60	for (uint i = 0; i < recipients.length; i++) {
61	transfer(recipients[i], amounts[i]); // Out-of-bounds if arrays differ in length
62	}
63	}
64
65	// SAFE
66	function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
67	require(recipients.length == amounts.length, "Length mismatch");
68	require(recipients.length <= MAX_BATCH_SIZE, "Batch too large");
69	// ...
70	}
71	```
72
73	Bounds Checking:
74
75	```solidity
76	// VULNERABLE: No upper bound on fee
77	function setFee(uint256 newFee) external onlyOwner {
78	fee = newFee; // Owner can set 100% fee, stealing all user funds
79	}
80
81	// SAFE
82	function setFee(uint256 newFee) external onlyOwner {
83	require(newFee <= MAX_FEE, "Fee too high"); // e.g., MAX_FEE = 1000 (10%)
84	fee = newFee;
85	}
86	```
87
88	### Input Validation Detection Algorithm
89
90	```
91	For each public/external function F:
92	For each parameter P:
93	1. Is P an address? → Check for require(P != address(0))
94	2. Is P an amount/value? → Check for require(P > 0) if zero is invalid
95	3. Is P an array? → Check for length validation and max size
96	4. Is P a percentage/rate? → Check for upper bound
97	5. Is P used as an index? → Check for bounds checking
98	6. Is P a deadline/timestamp? → Check for require(P > block.timestamp)
99
100	Flag any parameter without appropriate validation as:
101	- CRITICAL if parameter controls fund flow or access
102	- HIGH if parameter affects protocol state
103	- MEDIUM if parameter affects non-critical functionality
104	```
105
106	## Part 2: Arithmetic Vulnerability Analysis
107
108	### Pattern 1: Division-Before-Multiplication (Precision Loss)
109
110	```solidity
111	// VULNERABLE: Division first truncates, then multiplication amplifies error
112	uint256 result = (amount / totalShares) * price;
113	// If amount = 100, totalShares = 3: 100/3 = 33 (truncated from 33.33)
114	// 33 * price = less than expected
115
116	// SAFE: Multiply first, then divide
117	uint256 result = (amount * price) / totalShares;
118	// 100 * price / 3 = more precise (only one truncation at the end)
119	```
120
121	Detection:
122
123	```
124	For each arithmetic expression:
125	If division (/) appears BEFORE multiplication (*) in the same expression:
126	→ PRECISION LOSS: division-before-multiplication
127	Exception: If the division result is stored and intentionally used as a floored value
128	```
129
130	### Pattern 2: Rounding Direction Exploitation
131
132	In financial protocols, rounding direction determines who benefits:
133
134	```
135	Protocol-favorable rounding:
136	- Deposits: round DOWN shares (user gets fewer shares)
137	- Withdrawals: round DOWN ass

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input-arithmetic-safety

114stars23forks

View on GitHub

How to install input-arithmetic-safety?

quillai-network/quillshield_skills/input-arithmetic-safety

$npx -y skills add quillai-network/quillshield_skills --skill input-arithmetic-safety

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Input & Arithmetic Safety
2
3	Detect input validation failures (the #1 direct exploitation cause at 34.6% of all contract exploits) and arithmetic vulnerabilities that persist even with Solidity 0.8+ checked math — precision loss, rounding exploitation, unsafe casting, and share price manipulation.
4
5	## When to Use
6
7	- Auditing any contract with public/external functions accepting user-supplied parameters
8	- Reviewing DeFi protocols with fee calculations, share pricing, or exchange rates
9	- Analyzing vault/staking contracts for rounding or first-depositor attacks
10	- Checking contracts with `unchecked` blocks for overflow/underflow risks
11	- Verifying arithmetic in token minting, burning, and distribution logic
12
13	## When NOT to Use
14
15	- Access control analysis (use semantic-guard-analysis)
16	- Reentrancy detection (use reentrancy-pattern-analysis)
17	- Full multi-dimensional audit (use behavioral-state-analysis)
18
19	## Part 1: Input Validation Analysis
20
21	### Critical Missing Validations
22
23	Zero Address Check:
24
25	```solidity
26	// VULNERABLE: No zero address check
27	function setAdmin(address newAdmin) external onlyOwner {
28	admin = newAdmin; // Can set admin to address(0) — locking out admin forever
29	}
30
31	// SAFE
32	function setAdmin(address newAdmin) external onlyOwner {
33	require(newAdmin != address(0), "Zero address");
34	admin = newAdmin;
35	}
36	```
37
38	Zero Amount Check:
39
40	```solidity
41	// VULNERABLE: Allows zero-amount operations
42	function deposit(uint256 amount) external {
43	balances[msg.sender] += amount;
44	emit Deposit(msg.sender, amount);
45	// Zero deposit: wastes gas, pollutes events, may affect accounting
46	}
47
48	// SAFE
49	function deposit(uint256 amount) external {
50	require(amount > 0, "Zero amount");
51	balances[msg.sender] += amount;
52	}
53	```
54
55	Array Length Validation:
56
57	```solidity
58	// VULNERABLE: No length check
59	function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
60	for (uint i = 0; i < recipients.length; i++) {
61	transfer(recipients[i], amounts[i]); // Out-of-bounds if arrays differ in length
62	}
63	}
64
65	// SAFE
66	function batchTransfer(address[] calldata recipients, uint256[] calldata amounts) external {
67	require(recipients.length == amounts.length, "Length mismatch");
68	require(recipients.length <= MAX_BATCH_SIZE, "Batch too large");
69	// ...
70	}
71	```
72
73	Bounds Checking:
74
75	```solidity
76	// VULNERABLE: No upper bound on fee
77	function setFee(uint256 newFee) external onlyOwner {
78	fee = newFee; // Owner can set 100% fee, stealing all user funds
79	}
80
81	// SAFE
82	function setFee(uint256 newFee) external onlyOwner {
83	require(newFee <= MAX_FEE, "Fee too high"); // e.g., MAX_FEE = 1000 (10%)
84	fee = newFee;
85	}
86	```
87
88	### Input Validation Detection Algorithm
89
90	```
91	For each public/external function F:
92	For each parameter P:
93	1. Is P an address? → Check for require(P != address(0))
94	2. Is P an amount/value? → Check for require(P > 0) if zero is invalid
95	3. Is P an array? → Check for length validation and max size
96	4. Is P a percentage/rate? → Check for upper bound
97	5. Is P used as an index? → Check for bounds checking
98	6. Is P a deadline/timestamp? → Check for require(P > block.timestamp)
99
100	Flag any parameter without appropriate validation as:
101	- CRITICAL if parameter controls fund flow or access
102	- HIGH if parameter affects protocol state
103	- MEDIUM if parameter affects non-critical functionality
104	```
105
106	## Part 2: Arithmetic Vulnerability Analysis
107
108	### Pattern 1: Division-Before-Multiplication (Precision Loss)
109
110	```solidity
111	// VULNERABLE: Division first truncates, then multiplication amplifies error
112	uint256 result = (amount / totalShares) * price;
113	// If amount = 100, totalShares = 3: 100/3 = 33 (truncated from 33.33)
114	// 33 * price = less than expected
115
116	// SAFE: Multiply first, then divide
117	uint256 result = (amount * price) / totalShares;
118	// 100 * price / 3 = more precise (only one truncation at the end)
119	```
120
121	Detection:
122
123	```
124	For each arithmetic expression:
125	If division (/) appears BEFORE multiplication (*) in the same expression:
126	→ PRECISION LOSS: division-before-multiplication
127	Exception: If the division result is stored and intentionally used as a floored value
128	```
129
130	### Pattern 2: Rounding Direction Exploitation
131
132	In financial protocols, rounding direction determines who benefits:
133
134	```
135	Protocol-favorable rounding:
136	- Deposits: round DOWN shares (user gets fewer shares)
137	- Withdrawals: round DOWN ass

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