CVE-2025-20151 in IOS XE Catalyst SD-WAN
Summary
by MITRE • 05/07/2025
A vulnerability in the implementation of the Simple Network Management Protocol Version 3 (SNMPv3) feature of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to poll an affected device using SNMP, even if the device is configured to deny SNMP traffic from an unauthorized source or the SNMPv3 username is removed from the configuration.
This vulnerability exists because of the way that the SNMPv3 configuration is stored in the Cisco IOS Software and Cisco IOS XE Software startup configuration. An attacker could exploit this vulnerability by polling an affected device from a source address that should have been denied. A successful exploit could allow the attacker to perform SNMP operations from a source that should be denied. Note: The attacker has no control of the SNMPv3 configuration. To exploit this vulnerability, the attacker must have valid SNMPv3 user credentials. For more information, see the section of this advisory.
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Analysis
by VulDB Data Team • 08/05/2025
This vulnerability represents a critical flaw in the SNMPv3 implementation within Cisco IOS and IOS XE software platforms, specifically affecting how the system handles authentication and access control for network management operations. The issue stems from improper handling of SNMPv3 configuration data within the device's startup configuration file, creating a persistent security weakness that undermines the intended access controls. This vulnerability operates at the intersection of configuration management and network protocol security, where the system fails to properly validate access permissions during SNMP operations despite explicit denial rules being configured. The flaw fundamentally compromises the principle of least privilege by allowing unauthorized polling activities through legitimate authentication mechanisms.
The technical exploitation of this vulnerability requires an attacker to possess valid SNMPv3 credentials, which provides a baseline authentication mechanism that the system should properly enforce. However, the underlying implementation flaw allows bypassing the intended access control restrictions that should prevent polling from denied source addresses. This occurs because the SNMPv3 configuration data is stored and processed in a manner that does not adequately enforce the configured access control policies during active polling operations. The vulnerability demonstrates a classic configuration state inconsistency where the stored configuration reflects the intended security posture, but the operational behavior fails to respect those stored policies. This type of flaw falls under the CWE category of improper access control due to incorrect configuration handling, specifically CWE-284 for improper access control and CWE-255 for credentials management issues.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential reconnaissance and data exfiltration activities that could compromise network security. An authenticated attacker could leverage this weakness to perform unauthorized SNMP polling operations against network devices, potentially gathering sensitive operational data, configuration information, or system metrics that should remain protected. The vulnerability affects the integrity of the device's security configuration, as it allows bypassing explicit denial rules that administrators would have configured to prevent unauthorized access. This creates a persistent threat vector that could be exploited repeatedly without requiring additional authentication credentials, making it particularly dangerous in environments where SNMP is actively used for network management. The attack surface is significantly expanded as this vulnerability affects not just the initial access point but also the ongoing operational security posture of the affected devices.
Mitigation strategies for this vulnerability should focus on immediate configuration hardening and operational procedures to reduce the attack surface. Network administrators should implement additional access control measures beyond SNMPv3 authentication, such as implementing network segmentation, firewall rules, and access control lists that restrict SNMP traffic at the network level. The most effective immediate solution involves applying the vendor-provided security patches and updates that address the specific configuration handling flaw. Organizations should also conduct comprehensive audits of their SNMP configurations to identify and remediate any similar access control inconsistencies. The implementation of network monitoring and anomaly detection systems can help identify unauthorized SNMP polling activities that may indicate exploitation attempts. Additionally, security teams should consider implementing the principle of least privilege for SNMP access, ensuring that only essential personnel have valid SNMPv3 credentials and that these credentials are regularly rotated. This vulnerability highlights the importance of proper configuration management and the need for robust validation of security policies during operational execution, aligning with ATT&CK technique T1078 for valid accounts and T1046 for network service scanning.