CVE-2016-1432 in IOS XE
Summary
by MITRE
Cisco IOS XE 3.15S and 3.16S on cBR-8 Converged Broadband Router devices allows remote authenticated users to cause a denial of service (NULL pointer dereference and card restart) via a crafted SNMP request, aka Bug ID CSCuu68862.
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Analysis
by VulDB Data Team • 03/11/2019
Cisco IOS XE software versions 3.15S and 3.16S running on cBR-8 Converged Broadband Router devices contain a critical vulnerability that enables remote authenticated attackers to trigger a denial of service condition through carefully crafted SNMP requests. This vulnerability manifests as a NULL pointer dereference error that ultimately results in the complete restart of the affected card within the router. The flaw resides in the SNMP processing functionality of the IOS XE operating system, specifically when handling malformed or specially constructed SNMP packets. The vulnerability is classified under CWE-476 which represents NULL Pointer Dereference, a common software weakness that occurs when a program attempts to access memory through a pointer that has not been properly initialized or has been set to NULL. The issue affects the network infrastructure by potentially disrupting service availability and requiring manual intervention to restore normal operations. The cBR-8 Converged Broadband Router is designed for high-density broadband access and service delivery, making this vulnerability particularly concerning for service providers who rely on consistent network availability. Attackers exploiting this vulnerability need only valid SNMP credentials to execute the attack, which significantly lowers the barrier to exploitation compared to scenarios requiring physical access or more complex authentication bypass techniques. The impact extends beyond simple service disruption as the card restart process can cause temporary loss of network connectivity for services running on that specific hardware component. This vulnerability aligns with ATT&CK technique T1499.004 which covers Network Denial of Service attacks, specifically targeting network infrastructure devices to cause service interruption. The affected IOS XE versions represent a critical point of concern for organizations maintaining these routers in production environments, particularly those with limited network redundancy or those operating in mission-critical environments where service availability is paramount.
The technical implementation of this vulnerability involves the SNMP service component within IOS XE failing to properly validate incoming requests before attempting to process them. When a maliciously crafted SNMP packet is received, the system attempts to dereference a pointer that has not been properly initialized, leading to a system crash and subsequent restart of the affected card. This behavior demonstrates a classic software error where input validation is insufficient and error handling is inadequate to prevent system instability. The NULL pointer dereference occurs within the SNMP processing module, which is responsible for handling management communications between network devices and monitoring systems. The vulnerability affects the router's ability to maintain stable operation and can potentially be leveraged for repeated disruption attacks, where attackers could repeatedly send the crafted requests to maintain service degradation. The authentication requirement for exploitation adds a layer of complexity, as it requires attackers to first obtain valid SNMP credentials, which may be obtained through various means including credential theft, default credential usage, or social engineering attacks. The router's card restart behavior indicates that the system does not implement proper error recovery mechanisms to handle malformed inputs gracefully, instead allowing the error to propagate to a system-level failure that requires hardware-level intervention. This type of vulnerability is particularly dangerous in production networks where automated monitoring systems may not detect the card restart as a security incident, potentially masking the attack from security personnel. The vulnerability represents a failure in the principle of least privilege and input validation, where the system assumes that all incoming SNMP requests are valid and properly formatted without sufficient checks to prevent malformed data from causing system instability.
Organizations affected by this vulnerability should immediately implement network segmentation to limit access to SNMP services to only authorized management systems and personnel. The recommended mitigation strategy includes applying the latest security patches provided by Cisco, which address the NULL pointer dereference issue in the SNMP processing module. Network administrators should also configure SNMP access controls to restrict the source addresses that can communicate with the SNMP service and implement additional monitoring to detect unusual patterns of SNMP traffic that may indicate exploitation attempts. The implementation of network access control lists can help prevent unauthorized access to the SNMP service, while logging and alerting mechanisms should be configured to detect potential exploitation attempts. Security teams should also consider implementing network behavior analysis tools to identify anomalous SNMP traffic patterns that may indicate attempts to exploit this vulnerability. The vulnerability highlights the importance of maintaining up-to-date software versions and implementing proper network segmentation to limit the potential impact of such flaws. Organizations should also conduct regular vulnerability assessments to identify similar issues in other network devices and ensure that proper input validation and error handling mechanisms are in place throughout their network infrastructure. The cBR-8 platform's role in broadband service delivery makes this vulnerability particularly critical, as service interruptions can affect large numbers of end users and potentially result in significant financial and reputational damage for service providers. Additionally, the vulnerability demonstrates the need for robust error handling in network infrastructure software, where simple input validation failures can result in complete system instability and service disruption. The exploitation of this vulnerability aligns with the broader threat landscape where attackers increasingly target network infrastructure devices to cause maximum disruption with minimal effort.