CVE-2020-25445 in Ultimate Booking System Booking Core
Summary
by MITRE • 07/15/2021
The “Subscribe” feature in Ultimate Booking System Booking Core 1.7.0 is vulnerable to CSV formula injection. The input containing the excel formula is not being sanitized by the application. As a result when admin in backend download and open the csv, content of the cells are executed.
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Analysis
by VulDB Data Team • 07/18/2021
The vulnerability identified as CVE-2020-25445 affects the Ultimate Booking System Booking Core version 1.7.0, specifically targeting its "Subscribe" functionality. This represents a critical security flaw that falls under the category of CSV formula injection attacks, where malicious input can be executed when spreadsheet applications process the affected data. The vulnerability stems from inadequate input validation and sanitization within the application's backend processing mechanisms, creating an environment where user-supplied data containing spreadsheet formulas can be directly incorporated into exported CSV files without proper escaping or encoding.
The technical implementation of this vulnerability occurs when the application fails to sanitize user input before including it in CSV export functionality. When administrators download and open these CSV files using spreadsheet applications like Microsoft Excel or Google Sheets, any formula present in the cell data gets automatically executed by the spreadsheet application. This execution occurs because spreadsheet applications interpret certain characters and patterns as formula instructions, allowing attackers to inject malicious formulas such as formulae that can download and execute payloads, steal data, or perform other harmful actions. The vulnerability is particularly dangerous because it leverages the trust relationship between the spreadsheet application and the user, who typically expects CSV files to be simple data containers without executable content.
The operational impact of this vulnerability extends beyond simple data corruption or unauthorized access. An attacker who can influence the subscription data submitted through the vulnerable system can potentially execute arbitrary code on the administrator's machine when they open the exported CSV file. This creates a sophisticated attack vector that can be exploited through social engineering, where an attacker might send a specially crafted subscription request that, when processed and exported, would execute malicious code on the target system. The attack chain typically involves the attacker submitting malicious formula content in subscription forms, which gets stored in the database, then exported to CSV format, and finally executed when the administrator opens the file. This vulnerability can be classified under CWE-1237 - CSV Injection and maps to ATT&CK technique T1059.006 - Command and Scripting Interpreter: Python, though it can be exploited through various scripting environments depending on the target system configuration.
Mitigation strategies for this vulnerability require immediate implementation of input sanitization and output encoding mechanisms within the application's CSV export functionality. The system must escape or encode any potentially dangerous characters that could be interpreted as spreadsheet formulas, particularly the characters that initiate formulas such as equals sign, plus sign, minus sign, and other formula-specific operators. Organizations should implement proper data validation at multiple levels, including input sanitization, output encoding, and content security policies that prevent formula execution in spreadsheet applications. Additionally, administrators should be educated about the risks of opening CSV files from untrusted sources and should consider implementing security measures such as spreadsheet application configuration changes that disable automatic formula execution or implement sandboxed environments for CSV processing. The fix should also include implementing a comprehensive input validation framework that ensures all user-supplied data undergoes proper sanitization before being stored or exported, aligning with security best practices outlined in industry standards such as OWASP Top Ten and NIST cybersecurity guidelines.