CVE-2018-0189 in IOS
Summary
by MITRE
A vulnerability in the Forwarding Information Base (FIB) code of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, network attacker to cause a denial of service (DoS) condition. The vulnerability is due to a limitation in the way the FIB is internally representing recursive routes. An attacker could exploit this vulnerability by injecting routes into the routing protocol that have a specific recursive pattern. The attacker must be in a position on the network that provides the ability to inject a number of recursive routes with a specific pattern. An exploit could allow the attacker to cause an affected device to reload, creating a DoS condition. Cisco Bug IDs: CSCva91655.
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Analysis
by VulDB Data Team • 01/17/2020
The vulnerability identified as CVE-2018-0189 resides within the Forwarding Information Base implementation of Cisco IOS and IOS XE software versions, representing a critical denial of service weakness that can be exploited by unauthenticated network attackers. This flaw specifically targets the internal representation mechanism of recursive routes within the FIB subsystem, which serves as the core component responsible for maintaining routing tables and forwarding decisions in network devices. The vulnerability stems from insufficient validation and handling of recursive route patterns during the route processing lifecycle, creating an exploitable condition that can be triggered through carefully crafted route injections.
The technical exploitation of this vulnerability requires an attacker to possess network access and the capability to inject specific recursive route patterns into the routing protocol of an affected device. The flaw manifests when the FIB code encounters recursive routes that follow a particular pattern, causing the internal data structures to become corrupted or enter an unstable state. This occurs because the FIB implementation lacks proper bounds checking and validation mechanisms when processing recursive route references, allowing malicious route injections to trigger an overflow condition or memory corruption within the routing table management subsystem. The attack vector is particularly concerning as it does not require authentication credentials, making it accessible to any network entity capable of injecting routing updates.
The operational impact of this vulnerability extends beyond simple service disruption, as successful exploitation results in complete device reload or system crash, effectively creating a denial of service condition that can severely impact network availability and reliability. Network infrastructure devices affected by this vulnerability become temporarily unusable until manual intervention or automatic recovery mechanisms restore normal operation, potentially causing cascading failures throughout connected network segments. The DoS condition can be particularly devastating in mission-critical environments where network uptime is essential, as the device reload process typically requires network administrators to manually intervene, potentially leading to extended service outages and significant operational disruption.
Mitigation strategies for CVE-2018-0189 should focus on implementing proper route filtering and validation mechanisms at network boundaries, particularly through the deployment of route filtering policies that prevent the acceptance of recursive routes with suspicious patterns. Network administrators should also consider implementing monitoring solutions that can detect anomalous route injection patterns and trigger automated alerts when suspicious recursive route behaviors are detected. The Cisco recommended solution involves applying specific software patches and updates that modify the FIB route processing logic to include enhanced validation checks and proper bounds handling for recursive route entries. Organizations should also implement network segmentation strategies and access control measures to limit the potential attack surface and prevent unauthorized entities from injecting malicious routing information into the network infrastructure. This vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and maps to ATT&CK technique T1072 for the use of software libraries and system tools in executing malicious code within network infrastructure devices.