CVE-2026-20124 in IOS XE Software
Summary
by MITRE • 08/05/2026
A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS XE Software could allow an authenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition.
This vulnerability is due to improper error handling when parsing SNMP requests. This vulnerability affects all versions of SNMP — Versions 1, 2c, and 3. An attacker could exploit this vulnerability by sending a malformed SNMP request to an affected device. A successful exploit could allow the attacker to cause the device to reload unexpectedly. The attacker must have the SNMPv1 or v2c read-only or read-write community string or valid SNMPv3 user credentials on the affected device.
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Analysis
by VulDB Data Team • 08/05/2026
The vulnerability under examination represents a critical denial of service weakness within Cisco IOS XE Software's SNMP subsystem that poses significant operational risks to network infrastructure. This flaw manifests as improper error handling during SNMP request parsing, creating a condition where maliciously crafted requests can trigger unexpected system behavior. The vulnerability impacts all three major versions of SNMP protocols including versions 1, 2c, and 3, indicating a fundamental issue within the software's network management framework rather than protocol-specific weaknesses. From a cybersecurity perspective, this represents a privilege escalation concern since attackers must already possess valid credentials to exploit the vulnerability, though the impact remains severe enough to warrant immediate attention.
The technical implementation of this vulnerability stems from inadequate input validation and error handling mechanisms within the SNMP processing code path. When an affected device receives a malformed SNMP request, the system fails to properly handle the error condition, leading to a cascading failure that ultimately results in device reload operations. This behavior aligns with CWE-248, which describes improper exception handling in software systems where exceptions are not properly managed, causing unexpected program termination or system instability. The vulnerability's exploitation requires minimal network access as it operates over standard SNMP ports, typically UDP 161 for SNMP requests and TCP 162 for traps, making it particularly dangerous as it can be triggered remotely without physical access to the device.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromising network stability and availability. Network administrators face the challenge of maintaining uptime while managing a vulnerable system that can be exploited by authenticated attackers with minimal privileges. The fact that this affects all SNMP versions means that organizations cannot simply disable older protocols as a mitigation strategy, forcing them to implement more comprehensive solutions. This vulnerability particularly impacts enterprise networks where SNMP is extensively used for monitoring and management purposes, creating a scenario where network operations staff may inadvertently trigger the DoS condition while performing legitimate administrative tasks.
Organizations should prioritize immediate remediation through official Cisco security advisories and software updates that address the specific error handling flaws in the SNMP subsystem. The vulnerability's classification aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, though the implementation differs as it requires legitimate credentials rather than pure network reconnaissance. Network segmentation and access control measures can provide additional layers of defense by limiting which systems can communicate with SNMP-enabled devices. Furthermore, implementing monitoring solutions that detect unusual SNMP traffic patterns or device reload events can help identify exploitation attempts before they cause significant disruption to network operations. Security teams should also consider disabling SNMPv1 and v2c if SNMPv3 is available, as these older versions lack the authentication and encryption features that would otherwise prevent unauthorized access to the vulnerable subsystem.