CVE-2024-20373 in IOS
Summary
by MITRE • 11/15/2024
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.
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Analysis
by VulDB Data Team • 08/01/2025
This vulnerability represents a critical access control flaw in Cisco IOS and IOS XE software implementations that directly impacts network security posture through improper handling of SNMP IPv4 access control lists. The issue stems from a fundamental design gap where the software permits administrators to configure extended named IPv4 ACLs for SNMP server functionality without providing any warning about the lack of actual support for these extended ACLs. This creates a false sense of security as administrators believe their access controls are properly enforced while the system silently ignores the configured restrictions. The vulnerability specifically affects the SNMPv2c and SNMPv3 protocols where attackers can bypass configured ACLs through unauthorized polling operations, effectively undermining the intended network segmentation and access control policies. This flaw demonstrates a classic case of incomplete implementation where configuration options exist but do not function as expected, creating a security bypass mechanism that allows unauthorized access to network device management interfaces.
The technical implementation flaw manifests in how Cisco IOS and IOS XE software handle the SNMP server configuration process, where the system accepts extended IPv4 ACL configurations but fails to properly enforce them against incoming SNMP requests. This creates a scenario where the ACLs are configured but ineffective, allowing any unauthenticated remote attacker to perform SNMP polling operations regardless of the intended access restrictions. The vulnerability is particularly concerning because it operates silently without any error messages or warnings to alert administrators to the misconfiguration, making it difficult to detect and remediate. The attacker requires only a valid SNMP community string or user credentials to successfully exploit this vulnerability, which means that even if the network has strong authentication mechanisms in place, the ACL bypass can still be leveraged to gain unauthorized access to network device information and potentially perform further malicious activities.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential information disclosure and privilege escalation opportunities within network management systems. Attackers can leverage this vulnerability to gather sensitive network information through SNMP polling, potentially exposing network topology, device configurations, and operational details that could be used for further attacks. The vulnerability affects the core network management functionality and undermines the trust model that network administrators rely upon when implementing access controls. Additionally, the absence of IPv6 ACL support in this context indicates that the vulnerability is specifically tied to the IPv4 implementation and does not extend to IPv6 environments, which provides some limited mitigation but does not address the fundamental security gap in the IPv4 SNMP handling.
Mitigation strategies for this vulnerability should focus on immediate configuration remediation and ongoing monitoring of SNMP access controls. Network administrators must first disable or properly configure SNMP access controls to ensure that only authorized entities can perform SNMP operations, while also implementing additional monitoring of SNMP traffic to detect unauthorized access attempts. The recommended approach includes verifying that SNMP configurations properly enforce access controls and considering the implementation of network segmentation techniques that limit direct access to SNMP-enabled devices. Organizations should also review their SNMP community string management practices and ensure that strong authentication mechanisms are properly implemented. This vulnerability aligns with CWE-284 Access Control Bypass and can be mapped to ATT&CK techniques involving network service scanning and credential access through network protocols. The issue highlights the importance of proper input validation and access control enforcement in network management software implementations, emphasizing that configuration options must be properly enforced rather than simply accepted without verification.