CVE-2020-37221: Atomic Alarm Clock Buffer Overflow Flaw

CVE-2020-37221 Overview

CVE-2020-37221 is a stack-based buffer overflow [CWE-121] in Atomic Alarm Clock 6.3. The vulnerability exists in the Time Zones Clock configuration dialog, specifically in the display name textbox field. A local attacker can supply a malicious string that overflows a fixed-size stack buffer and overwrites the Structured Exception Handler (SEH) chain. The attacker leverages an encoded shellcode payload to bypass SafeSEH protections and execute arbitrary code with the privileges of the running application.

Critical Impact

Successful exploitation allows arbitrary code execution in the context of the Atomic Alarm Clock process, leading to full confidentiality, integrity, and availability compromise on the affected host.

Affected Products

• Atomic Alarm Clock 6.3
• Earlier versions sharing the same Time Zones Clock configuration component are likely affected
• Windows hosts running the vulnerable application binary

Discovery Timeline

• 2026-05-13 - CVE-2020-37221 published to the National Vulnerability Database (NVD)
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2020-37221

Vulnerability Analysis

The flaw is a classic stack overflow triggered through user-controlled input in the Time Zones Clock configuration UI. The application copies the display name string into a fixed-length stack buffer without enforcing length validation. When the supplied string exceeds the buffer size, adjacent stack memory is overwritten, including the saved SEH record. An attacker who controls the SEH handler pointer can redirect execution to attacker-supplied code when an exception is triggered.

The Common Weakness Enumeration identifier is [CWE-121] Stack-based Buffer Overflow. The EPSS score is 0.013%, indicating low observed exploitation activity, consistent with the local attack vector and niche application footprint.

Root Cause

The root cause is missing bounds checking on the display name input field. The application uses an unsafe string copy operation that does not validate the length of attacker-controlled Unicode input against the destination buffer. This permits linear stack corruption past the buffer boundary and into the SEH frame.

Attack Vector

Exploitation requires local access to interact with the Atomic Alarm Clock configuration interface. The attacker enters a crafted Unicode string into the display name textbox under Time Zones Clock settings. The payload contains padding to reach the SEH record, an overwritten Next SEH pointer, a pointer to a pop pop ret gadget outside SafeSEH-registered modules, and Venetian-encoded shellcode compatible with the Unicode transformation applied by the application. When an exception fires during input processing, control transfers through the corrupted SEH chain into the attacker shellcode.

The vulnerability mechanism and exploitation flow are documented in the Exploit-DB entry #48346 and the VulnCheck advisory on Atomic Alarm Clock SEH Unicode overflow.

Detection Methods for CVE-2020-37221

Indicators of Compromise

• Unexpected child processes spawned by the Atomic Alarm Clock executable on Windows endpoints
• Application crash events in the Windows Event Log referencing access violations or SEH chain corruption in the Atomic Alarm Clock process
• Modified or unusually large configuration files associated with Time Zones Clock display names

Detection Strategies

• Monitor process lineage for the Atomic Alarm Clock binary creating shells, scripting hosts such as cmd.exe or powershell.exe, or network utilities
• Inspect Windows Error Reporting (WER) crash dumps for exception records pointing to non-image memory regions, a signature of SEH overwrite exploitation
• Hunt for anomalous read or write operations on the application's configuration storage immediately preceding a crash

Monitoring Recommendations

• Enable Windows Defender Exploit Guard or equivalent exploit mitigation telemetry to capture SEH overwrite attempts
• Forward application crash telemetry and process creation events to a centralized logging or SIEM platform for correlation
• Baseline normal behavior of the Atomic Alarm Clock process and alert on deviations such as outbound network connections or memory allocation patterns consistent with shellcode staging

How to Mitigate CVE-2020-37221

Immediate Actions Required

• Restrict local interactive access to systems where Atomic Alarm Clock 6.3 is installed to trusted users only
• Remove or uninstall Atomic Alarm Clock 6.3 from endpoints that do not require it, especially shared or multi-user workstations
• Apply application control policies to block execution of the vulnerable binary until a vendor patch is available

Patch Information

No vendor patch is referenced in the available CVE data. Consult the VulnCheck advisory for vendor coordination status and check for updated releases from the application publisher before redeploying.

Workarounds

• Enable system-wide Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) through Windows Exploit Protection settings to raise the cost of SEH-based exploitation
• Configure Mandatory ASLR and SEHOP (Structured Exception Handler Overwrite Protection) for the Atomic Alarm Clock executable using Set-ProcessMitigation
• Run the application under a standard user account with no administrative rights to limit the impact of successful code execution

# Configuration example: enable SEHOP and DEP for the vulnerable binary on Windows
Set-ProcessMitigation -Name "AtomicAlarmClock.exe" -Enable SEHOP,DEP,ForceRelocateImages,BottomUp