CVE-2020-37109: aSc TimeTables DOS Vulnerability

CVE-2020-37109 Overview

CVE-2020-37109 is a denial of service vulnerability affecting aSc TimeTables 2020.11.4, a popular scheduling software used by educational institutions. The vulnerability allows attackers to crash the application by overwriting the Subject title field with an oversized buffer. By generating and pasting a 1000-character buffer into the Subject title input, attackers can trigger an application crash and cause system instability.

Critical Impact

Attackers can cause denial of service conditions in aSc TimeTables 2020.11.4 through buffer overflow in the Subject title field, disrupting scheduling operations.

Affected Products

• aSc TimeTables 2020.11.4
• aSc TimeTables 2020 (earlier versions potentially affected)

Discovery Timeline

• 2026-02-07 - CVE CVE-2020-37109 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2020-37109

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw exists in how aSc TimeTables handles user input in the Subject title field. When processing this input, the application fails to properly validate the length of data being written to the buffer, allowing attackers to supply oversized input that exceeds the allocated memory space.

The attack requires local access and user interaction, meaning an attacker must either have direct access to the system or trick a user into opening a maliciously crafted file or performing a specific action within the application.

Root Cause

The root cause of this vulnerability lies in inadequate input validation and boundary checking within the Subject title input handler. The application allocates a fixed-size buffer for storing the Subject title data but does not verify that incoming data fits within this boundary before copying it. This allows an attacker to overflow the buffer with excessive data, corrupting adjacent memory and causing the application to crash.

Attack Vector

The attack is executed locally and requires user interaction. An attacker can exploit this vulnerability by:

1. Generating a buffer of approximately 1000 characters or more
2. Accessing the Subject title field within the aSc TimeTables application
3. Pasting the oversized buffer into the field
4. The application attempts to process the input without proper bounds checking, resulting in a buffer overflow that crashes the application

The overflow condition leads to memory corruption that the application cannot recover from, resulting in a denial of service condition. Additional technical details are available in the Exploit-DB #48133 advisory.

Detection Methods for CVE-2020-37109

Indicators of Compromise

• Unexpected aSc TimeTables application crashes, particularly when editing Subject entries
• Windows Event Log entries indicating application faults in TimeTables.exe or related processes
• Memory access violation errors in system logs associated with the TimeTables application
• Presence of abnormally long strings in timetable data files

Detection Strategies

• Monitor for repeated application crashes of aSc TimeTables processes
• Implement endpoint detection rules to identify buffer overflow exploitation patterns
• Configure application crash monitoring through Windows Error Reporting
• Use SentinelOne's behavioral AI to detect memory corruption exploitation attempts

Monitoring Recommendations

• Enable verbose logging for aSc TimeTables if available
• Configure Windows Event Forwarding to collect application crash events centrally
• Deploy endpoint protection with memory protection capabilities
• Monitor for unusual file access patterns to TimeTables data files

How to Mitigate CVE-2020-37109

Immediate Actions Required

• Update aSc TimeTables to the latest available version from the official website
• Restrict local access to systems running aSc TimeTables to authorized users only
• Implement application whitelisting to prevent unauthorized modifications
• Review the VulnCheck Advisory for additional guidance

Patch Information

Users should check the aSc TimeTables official website for the latest version that addresses this vulnerability. It is recommended to upgrade from version 2020.11.4 to the most recent release available. Contact the vendor directly for specific patch availability information.

Workarounds

• Limit user access to the Subject title field functionality where possible
• Implement input validation at the network or application layer if using the software in a multi-user environment
• Consider running aSc TimeTables in an isolated environment or virtual machine to contain potential crashes
• Ensure regular backups of timetable data to minimize impact from potential denial of service attacks