Executive Summary

CVE-2026-30522 is a Business Logic vulnerability in SourceCodester Loan Management System version 1.0, specifically in the Plan Management component. The issue arises because the server does not properly validate the 'penalty_rate' parameter on the backend.

While the frontend interface prevents administrators from entering negative values in the 'Monthly Overdue Penalty' field, this restriction is not enforced on the server side. An authenticated attacker can bypass the client-side check by manipulating the HTTP POST request to submit a negative penalty rate.

This allows the attacker to create loan plans with negative penalty rates, which breaks the intended financial logic of overdue loan handling.

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Compliance Impact

The vulnerability allows manipulation of financial data by creating loan plans with negative penalty rates, which disrupts business logic and causes financial discrepancies.

Such financial inaccuracies and data integrity issues could potentially lead to non-compliance with regulations that require accurate financial record-keeping and data integrity, although no specific mention of GDPR, HIPAA, or other standards is provided.

Since the vulnerability affects financial calculations and data integrity, organizations using the affected system might face challenges in meeting compliance requirements related to financial accuracy and auditability.

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Mitigation Strategies

To mitigate this vulnerability immediately, ensure that server-side validation is implemented to enforce that the penalty_rate parameter cannot be negative.

Until a patch or update is applied, restrict administrative access to trusted users only and monitor HTTP POST requests to detect and block attempts to submit negative penalty_rate values.

Additionally, review and sanitize all inputs on the backend to prevent bypassing client-side restrictions.

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Impact Analysis

The vulnerability can cause disruption of business logic and financial discrepancies within the loan management system.

Specifically, because negative penalty rates are allowed, penalty calculations may produce incorrect results such as reducing the borrower's debt instead of applying a penalty.

This can lead to financial loss for the lending institution and corruption of data integrity.

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Detection Guidance

This vulnerability can be detected by monitoring HTTP POST requests to the endpoint ajax.php?action=save_plan and checking if the penalty_rate parameter contains negative values, which should not be allowed by the backend.

A practical way to test or detect this issue is to attempt sending a crafted POST request with a negative penalty_rate value to see if the server accepts it.

An example curl command to test this is:

• curl --compressed -s -i -X POST 'http://127.0.0.1:8082/ajax.php?action=save_plan' \
• -F "id=" \
• -F "months=12" \
• -F "interest_percentage=10" \
• -F "penalty_rate=-10" \
• -w "\nHTTP_STATUS:%{http_code}" \
• -H "Cookie: PHPSESSID=YOUR_COOKIE_HERE"

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