CVE-2016-4921 in Junos
Summary
by MITRE
By flooding a Juniper Networks router running Junos OS with specially crafted IPv6 traffic, all available resources can be consumed, leading to the inability to store next hop information for legitimate traffic. In extreme cases, the crafted IPv6 traffic may result in a total resource exhaustion and kernel panic. The issue is triggered by traffic destined to the router. Transit traffic does not trigger the vulnerability. This issue only affects devices with IPv6 enabled and configured. Devices not configured to process IPv6 traffic are unaffected by this vulnerability. This issue was found during internal product security testing. Juniper SIRT is not aware of any malicious exploitation of this vulnerability. Affected releases are Juniper Networks Junos OS 11.4 prior to 11.4R13-S3; 12.3 prior to 12.3R3-S4; 12.3X48 prior to 12.3X48-D30; 13.3 prior to 13.3R10, 13.3R4-S11; 14.1 prior to 14.1R2-S8, 14.1R4-S12, 14.1R8; 14.1X53 prior to 14.1X53-D28, 14.1X53-D40; 14.1X55 prior to 14.1X55-D35; 14.2 prior to 14.2R3-S10, 14.2R4-S7, 14.2R6; 15.1 prior to 15.1F2-S5, 15.1F5-S2, 15.1F6, 15.1R3; 15.1X49 prior to 15.1X49-D40; 15.1X53 prior to 15.1X53-D57, 15.1X53-D70.
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Analysis
by VulDB Data Team • 09/26/2022
The vulnerability described in CVE-2016-4921 represents a critical resource exhaustion flaw affecting Juniper Networks routers running Junos OS versions prior to specific security releases. This vulnerability operates through a sophisticated denial-of-service mechanism that specifically targets IPv6 processing capabilities within the router's forwarding plane. The flaw manifests when legitimate traffic destined to the router is processed through malformed IPv6 packets that exploit a deficiency in the routing table management system. The attack vector requires the router to be actively configured with IPv6 capabilities, making it a targeted issue for networks that utilize IPv6 addressing schemes. Security researchers identified this weakness during internal product security testing, highlighting the importance of comprehensive vulnerability assessment procedures within vendor environments.
The technical implementation of this vulnerability stems from an insufficient validation mechanism within the IPv6 packet processing pipeline of Junos OS. When the router receives specially crafted IPv6 traffic, the system fails to properly handle the packet structures, leading to progressive consumption of memory resources allocated for next hop information storage. This memory exhaustion occurs at the kernel level where routing decisions are made, causing the system to eventually reach a state where it cannot maintain routing table entries for legitimate traffic flows. The vulnerability's design allows for complete resource exhaustion through carefully constructed packets, potentially leading to kernel panic conditions that result in complete system failure. This represents a classic example of a resource exhaustion attack that leverages protocol implementation flaws rather than direct exploitation of code execution vulnerabilities.
The operational impact of CVE-2016-4921 extends beyond simple service disruption to encompass complete network infrastructure compromise. Network administrators face the challenge of maintaining routing stability when devices become unresponsive due to resource exhaustion, potentially causing cascading failures across interconnected networks. The vulnerability's specificity to devices with IPv6 enabled means that organizations with IPv6 configurations must immediately implement mitigation strategies, while those without IPv6 support remain unaffected. The attack requires only that the targeted router be configured to accept IPv6 traffic, making it particularly dangerous for enterprise networks that have adopted IPv6 for future-proofing their infrastructure. This vulnerability directly correlates to CWE-400, which addresses "Uncontrolled Resource Consumption" and specifically targets the kernel's memory management subsystem.
Mitigation strategies for CVE-2016-4921 require immediate implementation of firmware updates to affected Junos OS versions, with particular attention to the specific release notes provided by Juniper Networks. Organizations should prioritize updating all routers running vulnerable versions to their respective patched releases, ensuring that IPv6 processing capabilities are properly secured. Network administrators should also implement traffic filtering mechanisms at network boundaries to prevent malicious IPv6 packets from reaching vulnerable devices, though this approach provides only temporary protection. The vulnerability's classification under ATT&CK technique T1499.004 for "Endpoint Denial of Service" emphasizes the need for proactive security measures that include network segmentation and monitoring for unusual resource consumption patterns. Additionally, implementing comprehensive network monitoring solutions can help detect early signs of resource exhaustion before complete system failure occurs. Regular vulnerability assessments and security audits should be conducted to ensure that all network infrastructure components remain protected against similar implementation flaws in routing protocols and kernel modules.