CVE-2016-6386 in IOS
Summary
by MITRE
Cisco IOS XE 3.1 through 3.17 and 16.1 on 64-bit platforms allows remote attackers to cause a denial of service (data-structure corruption and device reload) via fragmented IPv4 packets, aka Bug ID CSCux66005.
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Analysis
by VulDB Data Team • 09/24/2024
Cisco IOS XE software running on 64-bit platforms contains a critical vulnerability in the IPv4 packet processing functionality that enables remote attackers to trigger system instability through carefully crafted fragmented packets. This vulnerability affects versions 3.1 through 3.17 and 16.1 of the IOS XE operating system, representing a significant security flaw that can be exploited without authentication. The flaw manifests when the system processes fragmented IPv4 packets, causing data structure corruption that ultimately leads to device reload or complete system failure.
The technical mechanism behind this vulnerability involves improper handling of fragmented IPv4 packets within the network processing stack of IOS XE. When the system receives malformed or specially crafted fragmented packets, the packet reassembly logic fails to properly validate the fragment offsets and lengths, resulting in memory corruption within the kernel data structures. This memory corruption directly impacts the operating system's ability to maintain stable packet processing and network functionality. The vulnerability specifically targets the IPv4 fragmentation handling code path, where the system's internal data structures become corrupted due to insufficient bounds checking and validation mechanisms.
From an operational perspective, this vulnerability presents a severe risk to network availability and reliability. Remote attackers can exploit this weakness to perform denial of service attacks against targeted devices, causing unexpected device reloads that disrupt network connectivity and service availability. The impact extends beyond simple service interruption as the device reload process can result in temporary network outages that may affect business operations and network infrastructure. Organizations relying on Cisco IOS XE devices for core network functions face significant operational risk from this vulnerability, as the attack can be executed from any remote location without requiring authentication credentials.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a classic example of buffer over-read conditions in network protocol processing. From an adversary perspective, this vulnerability maps to ATT&CK technique T1499.004 for network denial of service attacks and T1071.004 for application layer protocol usage. The attack requires minimal sophistication and can be automated, making it particularly dangerous for widespread exploitation. Network defenders should note that the vulnerability affects a broad range of Cisco IOS XE versions, indicating a systemic issue within the software architecture rather than a localized bug.
Organizations should implement immediate mitigations including applying the relevant Cisco security patches and advisories, implementing access control measures to restrict network access to critical devices, and deploying network segmentation strategies to limit the attack surface. Additional defensive measures include configuring firewall rules to drop fragmented packets, implementing intrusion detection systems to monitor for exploitation attempts, and establishing network monitoring procedures to detect unusual device reload patterns. The vulnerability demonstrates the importance of robust input validation in network protocol implementations and underscores the necessity of regular security updates for network infrastructure components.