CVE-2020-37182: Redir 3.3 Buffer Overflow Vulnerability

CVE-2020-37182 Overview

CVE-2020-37182 is a stack overflow vulnerability affecting Redir 3.3, a TCP port redirector utility commonly used in network proxy configurations. The vulnerability exists in the doproxyconnect() function where attackers can send oversized input to crash the application. By exploiting improper use of sprintf() without adequate length checking, attackers can overwrite memory and trigger a segmentation fault, resulting in immediate program termination.

Critical Impact

Remote attackers can cause denial of service by crashing Redir instances through network-based exploitation without authentication requirements.

Affected Products

• Redir 3.3

Discovery Timeline

• 2026-02-11 - CVE CVE-2020-37182 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2020-37182

Vulnerability Analysis

This stack-based buffer overflow vulnerability (CWE-121) occurs in the doproxyconnect() function within Redir 3.3. The vulnerability stems from the use of sprintf() to copy user-controlled input into a fixed-size stack buffer without proper bounds checking. When an attacker sends input exceeding the allocated buffer size, the data overwrites adjacent stack memory, corrupting the stack frame and ultimately causing a segmentation fault.

The network-accessible nature of this vulnerability means attackers can trigger the crash remotely without requiring any authentication or user interaction. While the immediate impact is limited to availability (denial of service), stack buffer overflows historically carry potential for more severe exploitation depending on system protections and memory layout.

Root Cause

The root cause is the unsafe use of sprintf() in the doproxyconnect() function. This function does not implement proper length validation before copying data into a stack-allocated buffer. The absence of bounds checking allows input larger than the buffer's capacity to overflow into adjacent stack memory, corrupting return addresses and other critical data structures.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can connect to a Redir instance and send specially crafted oversized input during the proxy connection process. The vulnerable sprintf() call processes this input without validation, causing the stack buffer to overflow and crash the application.

The exploitation requires no authentication and no user interaction, making it straightforward for attackers to repeatedly crash Redir services. Technical details and proof-of-concept code are available through Exploit-DB #47919.

Detection Methods for CVE-2020-37182

Indicators of Compromise

• Unexpected Redir process crashes or service interruptions
• Segmentation fault errors in system logs associated with Redir processes
• Abnormally large connection requests or payloads directed at Redir listening ports
• Repeated connection attempts from the same source IP followed by service failures

Detection Strategies

• Monitor Redir processes for unexpected terminations and automatic restart patterns
• Implement network intrusion detection rules to identify oversized payloads targeting Redir services
• Configure application-level logging to capture connection parameters before processing
• Deploy process monitoring to alert on segmentation faults in Redir instances

Monitoring Recommendations

• Enable core dump collection for Redir processes to facilitate post-incident analysis
• Monitor system logs for segmentation fault signals (SIGSEGV) associated with Redir
• Track Redir service availability metrics and alert on repeated crashes
• Implement network traffic analysis to detect anomalous input patterns

How to Mitigate CVE-2020-37182

Immediate Actions Required

• Upgrade Redir to a patched version that addresses the stack overflow vulnerability
• Implement network-level access controls to restrict connections to trusted sources only
• Consider deploying a network firewall or proxy in front of Redir to filter oversized requests
• Monitor for exploitation attempts while preparing to apply patches

Patch Information

Consult the GitHub Repository for Redir for the latest version and security updates. Review the VulnCheck Advisory on Redir DoS for additional guidance on remediation steps and version recommendations.

Workarounds

• Restrict network access to Redir services using firewall rules to limit exposure to trusted networks only
• Implement connection rate limiting to reduce the impact of repeated exploitation attempts
• Consider running Redir in a containerized or sandboxed environment to limit the impact of crashes
• Deploy a reverse proxy with input validation capabilities in front of Redir instances

# Example: Restrict Redir access using iptables
# Allow only trusted network 192.168.1.0/24 to access Redir on port 8080
iptables -A INPUT -p tcp --dport 8080 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP