CVE-2021-47781: Cmder Console Emulator Buffer Overflow

CVE-2021-47781 Overview

CVE-2021-47781 is a buffer overflow vulnerability affecting Cmder Console Emulator version 1.3.18. This vulnerability allows attackers to trigger a denial of service condition by exploiting improper input handling when processing maliciously crafted .cmd files. By creating a specially constructed command file containing repeated characters, an attacker can overwhelm the console emulator's buffer, causing the application to crash.

Critical Impact

Successful exploitation of this buffer overflow vulnerability results in denial of service, crashing the Cmder application and potentially disrupting user workflows and development environments.

Affected Products

• Cmder Console Emulator version 1.3.18

Discovery Timeline

• 2026-01-15 - CVE-2021-47781 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47781

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption flaw that occurs when the application writes data beyond the boundaries of allocated memory. In the context of Cmder Console Emulator 1.3.18, the vulnerability manifests when the application attempts to process .cmd files containing excessively long strings of repeated characters.

The local attack vector requires user interaction, as the victim must open or execute a malicious .cmd file. While the vulnerability does not compromise confidentiality or integrity, it has a high impact on availability, allowing attackers to reliably crash the application.

Root Cause

The root cause of this vulnerability lies in improper bounds checking within Cmder's file parsing routines. When processing .cmd files, the application fails to adequately validate the length of input strings before copying them into fixed-size buffers. This oversight allows specially crafted input containing repeated character sequences to exceed buffer boundaries, corrupting adjacent memory and ultimately causing the application to crash.

Attack Vector

The attack requires local access and user interaction to execute. An attacker would need to craft a malicious .cmd file with carefully constructed payloads containing repeated characters designed to overflow internal buffers. When a user opens or executes this file through Cmder, the buffer overflow condition is triggered.

The exploitation mechanism involves creating a .cmd file that contains strings exceeding the expected buffer size. When Cmder parses this file, the excessive input overflows the allocated buffer, leading to memory corruption and application crash. Detailed technical information about this vulnerability can be found in the Exploit-DB #50401 advisory.

Detection Methods for CVE-2021-47781

Indicators of Compromise

• Unexpected crashes or termination of Cmder Console Emulator processes
• Presence of suspicious .cmd files with abnormally large file sizes or repeated character patterns
• Application crash logs indicating memory access violations or segmentation faults in Cmder

Detection Strategies

• Monitor for Cmder application crashes or restarts, particularly when associated with .cmd file execution
• Implement file scanning rules to detect .cmd files with anomalously large content or suspicious repeated character patterns
• Deploy endpoint detection rules to alert on buffer overflow attack signatures targeting console emulator applications

Monitoring Recommendations

• Enable crash dump collection for Cmder processes to facilitate forensic analysis of potential exploitation attempts
• Configure application whitelisting to restrict execution of .cmd files from untrusted sources
• Implement file integrity monitoring on directories where command scripts are commonly stored

How to Mitigate CVE-2021-47781

Immediate Actions Required

• Upgrade Cmder Console Emulator to the latest available version from the GitHub Cmder Project
• Avoid opening .cmd files from untrusted or unknown sources
• Implement user awareness training about the risks of executing scripts from unverified sources

Patch Information

Organizations using Cmder Console Emulator version 1.3.18 should check the official GitHub Cmder Project repository for updated releases that address this buffer overflow vulnerability. Upgrading to a patched version is the recommended remediation approach.

Workarounds

• Restrict execution of .cmd files to trusted sources and known-good scripts only
• Use alternative console emulators until a patched version of Cmder is available
• Implement application sandboxing to contain potential crashes and prevent broader system impact

# Verify Cmder version and check for updates
cmder.exe /version
# Consider restricting .cmd file associations in enterprise environments
# until patch is applied