A vulnerability in the implementation of the Simple Network Management Protocol (SNMP) IPv4 access control list (ACL) feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to perform SNMP polling of an affected device, even if it is configured to deny SNMP traffic.
This vulnerability exists because Cisco IOS Software and Cisco IOS XE Software do not support extended IPv4 ACLs for SNMP, but they do allow administrators to configure extended named IPv4 ACLs that are attached to the SNMP server configuration without a warning message. This can result in no ACL being applied to the SNMP listening process. An attacker could exploit this vulnerability by performing SNMP polling of an affected device. A successful exploit could allow the attacker to perform SNMP operations that should be denied. The attacker has no control of the SNMP ACL configuration and would still need a valid SNMP version 2c (SNMPv2c) community string or SNMP version 3 (SNMPv3) user credentials. SNMP with IPv6 ACL configurations is not affected. For more information, see the section of this advisory.
| Software | From | Fixed in |
|---|---|---|
| cisco / ios_xe_sd-wan | 16.10.1 | 16.10.1.x |
| cisco / ios_xe_sd-wan | 16.9.3 | 16.9.3.x |
| cisco / ios_xe_sd-wan | 16.9.4 | 16.9.4.x |
| cisco / ios_xe_sd-wan | 16.10.2 | 16.10.2.x |
| cisco / ios_xe_sd-wan | 16.10.3 | 16.10.3.x |
| cisco / ios_xe_sd-wan | 16.10.3a | 16.10.3a.x |
| cisco / ios_xe_sd-wan | 16.10.6 | 16.10.6.x |
| cisco / ios_xe_sd-wan | 16.12.3 | 16.12.3.x |
| cisco / ios_xe_sd-wan | 16.12.1 | 16.12.1.x |
| cisco / ios_xe_sd-wan | 16.10.4 | 16.10.4.x |
| cisco / ios_xe_sd-wan | 16.10.5 | 16.10.5.x |
| cisco / ios_xe_sd-wan | 16.10.3b | 16.10.3b.x |
| cisco / ios_xe_sd-wan | 16.11.1s | 16.11.1s.x |
| cisco / ios_xe_sd-wan | 16.11.1a | 16.11.1a.x |
| cisco / ios_xe_sd-wan | 16.11.1f | 16.11.1f.x |
| cisco / ios_xe_sd-wan | 16.11.1b | 16.11.1b.x |
| cisco / ios_xe_sd-wan | 16.11.1 | 16.11.1.x |
| cisco / ios_xe_sd-wan | 16.11.1d | 16.11.1d.x |
| cisco / ios_xe_sd-wan | 16.12.4 | 16.12.4.x |
| cisco / ios_xe_sd-wan | 16.12.5 | 16.12.5.x |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.