CVE-2020-37126: Free Desktop Clock Buffer Overflow Flaw

CVE-2020-37126 Overview

Free Desktop Clock 3.0 contains a stack overflow vulnerability in the Time Zones display name input that allows attackers to overwrite Structured Exception Handler (SEH) registers. Attackers can exploit the vulnerability by crafting a malicious Unicode input that triggers an access violation and potentially execute arbitrary code.

Critical Impact

This stack overflow vulnerability enables SEH overwrite attacks, potentially allowing attackers to achieve arbitrary code execution on affected systems through crafted Unicode input.

Affected Products

• Free Desktop Clock 3.0

Discovery Timeline

• 2026-02-05 - CVE-2020-37126 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2020-37126

Vulnerability Analysis

This vulnerability (CWE-121: Stack-based Buffer Overflow) exists in the Time Zones display name input handling functionality of Free Desktop Clock 3.0. The application fails to properly validate the length of user-supplied Unicode input when processing time zone display names, resulting in a classic stack-based buffer overflow condition.

When exploited, the overflow allows an attacker to corrupt memory beyond the intended buffer boundaries, specifically targeting the Structured Exception Handler (SEH) chain stored on the stack. By overwriting SEH records with attacker-controlled values, an adversary can redirect program execution flow when an exception is triggered.

The local attack vector requires user interaction, as a victim must be convinced to input or import malicious data into the Time Zones display name field. Once the crafted Unicode payload is processed, it triggers an access violation that can be leveraged for code execution.

Root Cause

The root cause of this vulnerability is insufficient input validation and boundary checking in the Time Zones display name input handler. The application allocates a fixed-size buffer on the stack to store the user-provided display name but fails to enforce length restrictions before copying Unicode data into this buffer. This allows attackers to supply an oversized input that overflows the allocated buffer space.

Attack Vector

The attack requires local access to the vulnerable application. An attacker must craft a specially formatted Unicode string designed to:

1. Overflow the stack buffer allocated for the Time Zones display name
2. Overwrite the SEH chain with controlled addresses
3. Trigger an exception that invokes the corrupted exception handler
4. Redirect execution flow to attacker-controlled shellcode

The vulnerability leverages Unicode-based overflow techniques, which can complicate exploitation but also bypass certain character filters. Additional technical details are available in the Exploit-DB #48314 entry and the Vulncheck Advisory for Free Desktop Clock.

Detection Methods for CVE-2020-37126

Indicators of Compromise

• Unexpected crashes or access violations in Free Desktop Clock 3.0
• Anomalous process behavior or child process spawning from the Free Desktop Clock application
• Evidence of SEH chain manipulation in crash dumps or memory analysis
• Presence of unusually long Unicode strings in application configuration or input files

Detection Strategies

• Monitor for application crashes involving Free Desktop Clock with access violation exceptions
• Implement endpoint detection rules for SEH overwrite exploitation patterns
• Deploy SentinelOne behavioral analysis to detect anomalous memory corruption attempts
• Review application logs for evidence of oversized input processing in time zone configurations

Monitoring Recommendations

• Enable detailed crash logging and reporting for desktop applications
• Implement Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) monitoring
• Configure SentinelOne agents to alert on suspicious memory manipulation techniques
• Audit systems for the presence of Free Desktop Clock 3.0 installations

How to Mitigate CVE-2020-37126

Immediate Actions Required

• Remove or disable Free Desktop Clock 3.0 from all systems until a patched version is available
• Restrict user access to the Time Zones configuration functionality if continued use is necessary
• Ensure DEP and ASLR are enabled on all systems running the vulnerable software
• Consider migrating to alternative desktop clock utilities that are actively maintained

Patch Information

No official vendor patch information is currently available for this vulnerability. Users should check the Drive Software Homepage for any future security updates. Given the age of this software (version 3.0), users are strongly encouraged to consider alternative solutions that receive regular security updates.

Workarounds

• Uninstall Free Desktop Clock 3.0 from affected systems
• If removal is not possible, restrict access to the application to trusted users only
• Enable exploit mitigation technologies such as DEP, ASLR, and SEHOP at the operating system level
• Deploy endpoint protection solutions like SentinelOne to detect and block exploitation attempts
• Avoid importing or copying time zone configuration data from untrusted sources

# Verify DEP and ASLR status on Windows systems
# Check DEP status via PowerShell
Get-CimInstance -ClassName Win32_OperatingSystem | Select-Object DataExecutionPrevention_Available, DataExecutionPrevention_SupportPolicy

# Enable SEHOP via registry (requires administrator privileges)
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\kernel" /v DisableExceptionChainValidation /t REG_DWORD /d 0 /f