CVE-2026-89147
Received Received - Intake

Denial of Service in Net-SNMP SMUX Module

Publication date: 2026-09-11

Last updated on: 2026-09-11

Assigner: VulnCheck

Description
Net-SNMP through 5.9.5.2 contains a denial of service vulnerability in the SMUX module where smux_accept() performs an unauthenticated blocking read without timeout on newly accepted connections. An unauthenticated remote client can connect to the SMUX listener and send no data, causing the single-threaded snmpd main loop to block indefinitely and suspend all SNMP processing.

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Meta Information

Published
2026-09-11
Last Modified
2026-09-11
Generated
2026-09-11
AI Q&A
2026-09-11
EPSS Evaluated
N/A
NVD
CVE-2026-89147
EUVD
EUVD-2026-76036

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
net-snmp net-snmp to 5.9.5.2 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.
CWE-1088 The code has a synchronous call to a remote resource, but there is no timeout for the call, or the timeout is set to infinite.

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Executive Summary

This vulnerability is a denial of service flaw in Net-SNMP through version 5.9.5.2. The SMUX module's smux_accept() function performs an unauthenticated blocking read without timeout on new connections. An attacker can connect to the SMUX listener and send no data, causing the single-threaded snmpd main loop to block indefinitely and stop all SNMP processing.

Detection Guidance

Check if the SMUX listener is active on TCP port 199 using netstat or ss. Run 'netstat -tulnp | grep 199' or 'ss -tulnp | grep 199'. If the port is open and bound to all interfaces, the system may be vulnerable. Monitor snmpd logs for blocked requests or timeouts during SNMP processing.

Impact Analysis

This vulnerability allows an unauthenticated remote attacker to cause a denial of service by blocking all SNMP processing. This halts monitoring capabilities, prevents legitimate SNMP requests from being processed, and disrupts system management functions that rely on SNMP.

Mitigation Strategies

Disable the SMUX listener if not needed by editing snmpd.conf and removing any 'smuxpeer' directives. Restart snmpd with 'systemctl restart snmpd'. If SMUX is required, apply patches from Net-SNMP or upgrade to a version beyond 5.9.5.2. Block external access to TCP port 199 using a firewall.

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