CVE-2016-6355 in IOS XR
Summary
by MITRE
Memory leak in Cisco IOS XR 5.1.x through 5.1.3, 5.2.x through 5.2.5, and 5.3.x through 5.3.2 on ASR 9001 devices allows remote attackers to cause a denial of service (control-plane protocol outage) via crafted fragmented packets, aka Bug ID CSCux26791.
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Analysis
by VulDB Data Team • 03/25/2019
The vulnerability described in CVE-2016-6355 represents a critical memory leak issue affecting Cisco IOS XR software versions across multiple release streams including 5.1.x through 5.1.3, 5.2.x through 5.2.5, and 5.3.x through 5.3.2 on ASR 9001 devices. This flaw resides within the control-plane protocol handling mechanisms of the operating system, specifically manifesting when the system processes crafted fragmented network packets. The vulnerability operates at the network protocol level where the device's memory management fails to properly handle memory allocation and deallocation during packet processing, creating a persistent memory consumption issue that gradually depletes available system resources.
The technical implementation of this vulnerability exploits the fragmentation handling routines within the IOS XR control plane protocols, particularly affecting the routing and forwarding functions that maintain the device's operational stability. When remote attackers send carefully constructed fragmented packets to the affected ASR 9001 routers, the system's memory management routines fail to properly release allocated memory blocks after processing these packets, leading to a gradual accumulation of unreleased memory segments. This memory leak directly impacts the device's ability to maintain stable control-plane operations, as the continuous consumption of memory resources eventually leads to system instability and complete service disruption.
The operational impact of CVE-2016-6355 manifests as a denial of service condition that can severely compromise network infrastructure availability. The control-plane protocol outage affects the device's routing functions, packet forwarding capabilities, and overall system responsiveness, potentially causing complete network disruption for services relying on the affected ASR 9001 devices. The vulnerability's remote exploitability means that attackers can trigger the memory leak from external network locations without requiring physical access or authentication credentials, making it particularly dangerous in production environments where network availability is critical. This flaw directly relates to CWE-401, which addresses improper management of memory allocation and deallocation, and aligns with ATT&CK technique T1499.004 for network denial of service attacks.
Mitigation strategies for this vulnerability require immediate implementation of Cisco's security advisory patches and software updates addressing the specific memory leak conditions in the affected IOS XR versions. Network administrators should implement packet filtering rules to limit fragmented packet processing and consider rate limiting mechanisms to prevent rapid memory exhaustion attacks. Additionally, monitoring systems should be deployed to track memory usage patterns and detect anomalous consumption that may indicate exploitation attempts. The recommended approach involves applying the vendor-provided security patches while implementing network segmentation and access controls to limit potential attack vectors. Organizations should also establish proactive monitoring protocols to identify early signs of memory leak conditions and maintain robust backup and recovery procedures to ensure rapid restoration of services during potential exploitation events.