Net-SNMP vulnerability in SMUX module allows remote denial of service on Ubuntu

Ubuntu has released security updates to address a vulnerability in the Net-SNMP suite, specifically affecting the SMUX (Service Management Using SNMP) module. The flaw allows an unauthenticated remote attacker to send specially crafted network traffic that causes the service to handle new connections incorrectly.

This vulnerability results in a denial of service (DoS) by causing Net-SNMP to block indefinitely and stop responding. The fix is available for three major Ubuntu Long Term Support (LTS) releases: 26.04, 24.04, and 22.04. Users are advised to perform a standard system update to apply the patched versions of libsnmp, snmp, and snmpd.

Technical details of CVE-2026-89147

• Vulnerability Type: Denial of Service (DoS) via improper connection handling.
• Impact: The service enters an indefinite blocking state, rendering the SNMP server unresponsive to legitimate management requests.
• Fixed Versions: Includes libsnmp40t64/snmp/snmpd version 5.9.4+dfsg-2ubuntu3.1 (26.04), 5.9.4+dfsg-1.1ubuntu3.3 (24.04), and 5.9.1+dfsg-1ubuntu2.10 (22.04).

Why it matters

Since Net-SNMP is a standard tool for monitoring and managing network devices and servers, this vulnerability poses a risk to infrastructure stability. System administrators managing large-scale deployments via SNMP must prioritize these updates to prevent remote attackers from disabling network monitoring capabilities.