CVE-2024-20467 in IOS XE
Summary
by MITRE • 09/25/2024
A vulnerability in the implementation of the IPv4 fragmentation reassembly code in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to improper management of resources during fragment reassembly. An attacker could exploit this vulnerability by sending specific sizes of fragmented packets to an affected device or through a Virtual Fragmentation Reassembly (VFR)-enabled interface on an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
Note: This vulnerability affects Cisco ASR 1000 Series Aggregation Services Routers and Cisco cBR-8 Converged Broadband Routers if they are running Cisco IOS XE Software Release 17.12.1 or 17.12.1a.
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Analysis
by VulDB Data Team • 10/04/2024
This vulnerability resides within the IPv4 fragmentation reassembly functionality of Cisco IOS XE Software, representing a critical flaw that undermines network device stability and availability. The issue manifests when the software fails to properly manage system resources during the process of reassembling fragmented IP packets, creating a potential attack vector for remote unauthenticated adversaries. The vulnerability specifically impacts Cisco ASR 1000 Series Aggregation Services Routers and Cisco cBR-8 Converged Broadband Routers operating on Cisco IOS XE Software releases 17.12.1 or 17.12.1a, making these devices particularly susceptible to targeted disruption attempts. The flaw demonstrates characteristics consistent with resource exhaustion and improper state management patterns commonly found in network protocol implementations.
The technical exploitation of this vulnerability occurs through carefully crafted fragmented packet sequences that trigger the flawed reassembly logic within the IOS XE software stack. Attackers can leverage this by transmitting specific sized fragments either directly to the affected device or through Virtual Fragmentation Reassembly enabled interfaces, which are designed to handle fragmented traffic more efficiently. The improper resource management during this process leads to a condition where the system's memory or processing capabilities become exhausted, ultimately forcing the device to undergo an unexpected reload cycle. This behavior aligns with CWE-400 patterns related to resource exhaustion and improper handling of network packet reassembly states, which are fundamental to maintaining system stability in network infrastructure devices.
The operational impact of this vulnerability extends beyond simple service interruption, as it creates a persistent threat to network availability and reliability for organizations relying on affected Cisco hardware. When successfully exploited, the device reload caused by the vulnerability results in complete service disruption until manual intervention or automatic recovery mechanisms restore functionality. Network administrators face the challenge of maintaining uptime for critical infrastructure while dealing with potential denial of service attacks that can be executed without authentication credentials or specialized knowledge. This vulnerability particularly affects service providers and enterprise networks where these routers serve as core aggregation points, making the potential for widespread disruption significant. The attack vector's accessibility through standard network traffic means that even basic network reconnaissance could reveal the vulnerability's presence and exploitability.
Mitigation strategies for this vulnerability should focus on immediate protective measures while implementing longer-term solutions to address the root cause. Network administrators should consider disabling Virtual Fragmentation Reassembly functionality on affected interfaces if the feature is not essential for operations, as this can prevent exploitation through the primary attack path. Additionally, implementing ingress filtering and rate limiting mechanisms can help reduce the effectiveness of fragmentation-based attacks by controlling the volume and characteristics of incoming fragmented packets. Cisco has released software updates addressing this vulnerability in newer IOS XE releases, making patch management a critical component of remediation efforts. Organizations should also implement monitoring solutions to detect anomalous fragmentation patterns that could indicate exploitation attempts, as well as establish incident response procedures specifically designed to handle DoS conditions affecting core network infrastructure. The vulnerability's classification under ATT&CK technique T1499.004 for network denial of service aligns with established threat modeling frameworks that emphasize protecting network infrastructure from resource exhaustion attacks.