CVE-2015-0694 in Aggregate Services Router 9000 ASR9K
Summary
by MITRE
Cisco ASR 9000 devices with software 5.3.0.BASE do not recognize that certain ACL entries have a single-host constraint, which allows remote attackers to bypass intended network-resource access restrictions by using an address that was not supposed to have been allowed, aka Bug ID CSCur28806.
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Analysis
by VulDB Data Team • 05/03/2022
The vulnerability identified as CVE-2015-0694 affects Cisco ASR 9000 series routers operating with software version 5.3.0.BASE and represents a significant access control flaw that undermines network security policies. This issue stems from the router's improper handling of Access Control List (ACL) entries that should enforce single-host constraints, creating a bypass mechanism that allows unauthorized network access. The vulnerability specifically impacts devices configured with ACLs that are intended to restrict access to specific hosts or IP addresses, but due to the software flaw, these restrictions are not properly enforced.
The technical root cause of this vulnerability lies in the ACL processing logic within the Cisco IOS XR operating system that runs on ASR 9000 devices. When ACL entries are configured with single-host constraints, the software fails to correctly interpret these rules, leading to a situation where certain IP addresses that should be denied access are incorrectly allowed. This misinterpretation occurs during the packet filtering process where the router evaluates incoming traffic against configured ACL rules. The flaw manifests when the router's ACL engine does not properly validate that specific address constraints are being enforced, allowing traffic from addresses that should have been restricted to pass through the network boundary.
From an operational perspective, this vulnerability presents a serious risk to network security infrastructure as it enables remote attackers to bypass access controls that are fundamental to network protection. An attacker could exploit this flaw to gain unauthorized access to network resources that should be restricted to specific hosts or IP ranges. The impact extends beyond simple unauthorized access, as it undermines the entire network segmentation strategy that organizations rely on to contain potential security breaches. Network administrators who depend on ACLs for traffic control and access restriction may find their security policies effectively nullified, potentially allowing lateral movement within the network or access to sensitive systems that should be protected.
The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and represents a classic case of privilege escalation through misconfigured access controls. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and lateral movement, as attackers can exploit the flawed ACL enforcement to move beyond their initial access boundaries. The remote nature of the attack means that threat actors can exploit this vulnerability from outside the network perimeter without requiring physical access or local credentials. This characteristic makes the vulnerability particularly dangerous as it can be exploited by attackers who are not directly connected to the network infrastructure.
Organizations should implement immediate mitigations including applying the relevant Cisco security patches and updates that address this ACL processing flaw. Network administrators should conduct comprehensive audits of their ACL configurations to identify any entries that may be vulnerable to this bypass mechanism. Additional defensive measures include implementing redundant access control mechanisms, monitoring network traffic for unusual patterns that might indicate exploitation attempts, and reviewing network segmentation policies to ensure that critical resources are protected through multiple layers of security controls. The vulnerability also underscores the importance of regular security assessments and maintaining up-to-date network device firmware to protect against known security flaws that could compromise network integrity and access control policies.