cwe-191-integer-underflow

name	cwe-191-integer-underflow
description	Use this skill when you need to remediate CWE-191 (Integer Underflow) vulnerabilities in Java code. Triggers on SAST findings, security reviews, or when fixing integer underflow issues.
version	1.0.0
license	MIT
tags	["security","java","cwe-191","remediation","sast"]

CWE-191 Integer Underflow

Description

Integer Underflow

Reference: https://cwe.mitre.org/data/definitions/191.html

OWASP Category: A03:2021 – Injection

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Vulnerable Pattern

❌ Example 1: Vulnerable Pattern

// VULNERABLE: Possible underflow
int balance = user.getBalance();
int withdrawal = request.getAmount();
user.setBalance(balance - withdrawal); // Could underflow

Why it's vulnerable: This pattern is vulnerable to Integer Underflow

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Deterministic Fix

✅ Secure Implementation: Secure Implementation

// SECURE: Check for underflow
int balance = user.getBalance();
int withdrawal = request.getAmount();
if (withdrawal > balance) {
    throw new IllegalArgumentException("Insufficient funds");
}
// Or use Math.subtractExact for automatic overflow detection
user.setBalance(Math.subtractExact(balance, withdrawal));

Why it's secure: Implements proper protection against Integer Underflow

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Detection Pattern

Look for these patterns in your codebase:

# Find subtraction operations
grep -rn "balance.*-\\|index.*-" --include="*.java"

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Remediation Steps

1. Validate input values before arithmetic

2. Use Math.subtractExact() for automatic overflow/underflow detection

3. Check bounds before array index calculations

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Key Imports

import java.lang.Math;

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Verification

After remediation:

• Run SAST scanner to confirm vulnerability is resolved

• Review all instances of the vulnerable pattern

• Add unit tests that verify the secure implementation

• Check for similar patterns in related code

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Trigger Examples

Fix CWE-191 vulnerability
Resolve Integer Underflow issue
Secure this Java code against integer underflow
SAST reports CWE-191

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Common Vulnerable Locations

Layer	Files	Patterns

| Controller | *Controller.java | User input handling |

| Service | *Service.java | Business logic |

| Repository | *Repository.java | Data access |

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References

• CWE-191: Integer Underflow

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Source: Generated by Java CWE Security Skills Generator Last Updated: 2026-03-07