CVE-2020-37127: Dnsmasq-utils Buffer Overflow DoS Vulnerability

CVE-2020-37127 Overview

CVE-2020-37127 is a buffer overflow vulnerability in the dhcp_release utility of Dnsmasq-utils version 2.79-1. This vulnerability allows attackers to cause a denial of service condition by supplying excessive input to the utility. When an attacker sends a crafted input string longer than 16 characters, the dhcp_release process can be terminated with a core dump, effectively disrupting DHCP release operations on affected systems.

Critical Impact

Local attackers can crash the dhcp_release utility through buffer overflow, causing denial of service and potential disruption to DHCP management operations on affected Linux systems.

Affected Products

• Dnsmasq-utils 2.79-1
• Linux distributions packaging vulnerable dnsmasq versions
• Systems utilizing the dhcp_release utility for DHCP lease management

Discovery Timeline

• 2026-02-05 - CVE CVE-2020-37127 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2020-37127

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The dhcp_release utility fails to properly validate the length of user-supplied input before copying it into a fixed-size buffer. When input exceeding 16 characters is provided, the data overflows the buffer boundaries, corrupting adjacent stack memory and leading to process termination.

The attack requires local access to execute the vulnerable utility with malicious input. While the immediate impact is limited to denial of service through process crashes, buffer overflow vulnerabilities can potentially be leveraged for more severe attacks depending on the specific memory layout and exploitation techniques.

Root Cause

The root cause is insufficient bounds checking in the dhcp_release utility's input handling routines. The code allocates a fixed-size buffer (16 characters) but does not enforce length restrictions on user input before copying data into this buffer. This classic buffer overflow pattern results from missing input validation, allowing attackers to write beyond allocated memory boundaries.

Attack Vector

The attack vector is local, requiring an attacker to have access to execute the dhcp_release utility on the target system. The attacker crafts an input string exceeding the 16-character buffer limit and passes it to the utility. This triggers a stack-based buffer overflow that corrupts the stack frame, causing the process to crash with a segmentation fault and generate a core dump.

The vulnerability can be exploited by any user with permissions to execute the dhcp_release utility. A proof-of-concept exploit demonstrating this vulnerability is publicly available on Exploit-DB #48301. The attack does not require special privileges beyond execution access to the vulnerable binary.

Detection Methods for CVE-2020-37127

Indicators of Compromise

• Unexpected core dumps from the dhcp_release process in system logs
• Repeated crashes or restarts of the dhcp_release utility
• Segmentation fault messages associated with dnsmasq utilities in /var/log/syslog or system journal
• Abnormal command-line arguments to dhcp_release containing excessively long strings

Detection Strategies

• Monitor system logs for dhcp_release process crashes and core dumps
• Implement file integrity monitoring on dnsmasq-utils binaries to detect tampering
• Configure auditd rules to log executions of the dhcp_release utility with unusual argument lengths
• Deploy endpoint detection solutions to identify buffer overflow exploitation attempts

Monitoring Recommendations

• Enable core dump collection and analysis to capture evidence of exploitation attempts
• Set up alerts for repeated process failures of DHCP management utilities
• Monitor for unusual activity patterns around DHCP infrastructure components
• Review system audit logs for suspicious command-line activity targeting dnsmasq utilities

How to Mitigate CVE-2020-37127

Immediate Actions Required

• Update dnsmasq-utils to a patched version that addresses the buffer overflow
• Restrict execution permissions on the dhcp_release utility to authorized administrators only
• Implement access controls to limit which users can interact with DHCP management tools
• Consider disabling or removing the dhcp_release utility if not required for operations

Patch Information

Users should check for updated packages from their Linux distribution. Refer to the Ubuntu dnsmasq Source Package for version information and updates. Additional details are available in the VulnCheck dnsmasq Advisory.

Workarounds

• Restrict access to the dhcp_release binary using file system permissions (e.g., chmod 750)
• Implement wrapper scripts that validate input length before passing to dhcp_release
• Use AppArmor or SELinux policies to confine the dhcp_release utility
• Consider alternative DHCP management tools until a patch is applied

# Restrict dhcp_release permissions to root only
sudo chmod 700 /usr/bin/dhcp_release
sudo chown root:root /usr/bin/dhcp_release

# Verify the restriction
ls -la /usr/bin/dhcp_release