CVE-2021-0217 in Junos
Summary
by MITRE • 01/16/2021
A vulnerability in processing of certain DHCP packets from adjacent clients on EX Series and QFX Series switches running Juniper Networks Junos OS with DHCP local/relay server configured may lead to exhaustion of DMA memory causing a Denial of Service (DoS). Over time, exploitation of this vulnerability may cause traffic to stop being forwarded, or to crashing of the fxpc process. When Packet DMA heap utilization reaches 99%, the system will become unstable. Packet DMA heap utilization can be monitored through the following command: user@junos# request pfe execute target fpc0 timeout 30 command "show heap" ID Base Total(b) Free(b) Used(b) % Name -- ---------- ----------- ----------- ----------- --- ----------- 0 213301a8 536870488 387228840 149641648 27 Kernel 1 91800000 8388608 3735120 4653488 55 DMA 2 92000000 75497472 74452192 1045280 1 PKT DMA DESC 3 d330000 335544320 257091400 78452920 23 Bcm_sdk 4 96800000 184549376 2408 184546968 99 Packet DMA
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Analysis
by VulDB Data Team • 02/15/2021
This vulnerability represents a critical denial of service condition affecting juniper networks ex series and qfx series switches operating junos os with dhcp local or relay server configurations. The flaw specifically targets the processing of dhcp packets originating from adjacent network clients, creating a scenario where malicious or malformed dhcp traffic can systematically consume available direct memory access dma memory resources. The vulnerability operates through the packet dma heap utilization mechanism, where normal dhcp packet processing triggers memory allocation that gradually depletes the available dma memory pool. When the packet dma heap utilization reaches 99 percentage, the system experiences severe instability leading to complete traffic forwarding cessation or fxpc process crashes. This represents a classic resource exhaustion attack vector that leverages legitimate network protocols to create system instability. The vulnerability is particularly concerning because it operates at the hardware level through the fpc process and packet dma mechanisms, making it difficult to detect and mitigate through traditional network security measures. The impact extends beyond simple service disruption as the system becomes increasingly unstable as utilization approaches critical thresholds, potentially leading to complete system failure or reboot cycles.
The technical implementation of this vulnerability stems from insufficient memory management during dhcp packet processing within the switch's packet forwarding engine. The system's failure to properly validate or limit memory allocation during dhcp packet handling creates a predictable exploitation pattern where repeated dhcp traffic can cause progressive memory depletion. The underlying architecture relies on fixed memory pools managed through the packet dma heap structures, which are not adequately protected against excessive allocation patterns. When dhcp packets are processed through the local or relay server functions, they trigger memory allocation within the dma heap that grows progressively until reaching the 99% utilization threshold. This memory exhaustion directly impacts the packet forwarding capabilities of the switch because the fpc process depends on adequate dma memory for packet processing operations. The vulnerability demonstrates poor input validation and resource management practices that allow legitimate network protocols to be weaponized for denial of service attacks. The specific command used to monitor heap utilization provides insight into the memory allocation patterns and helps identify when the system is approaching critical failure states.
Operational impact of this vulnerability extends beyond immediate service disruption to include potential business continuity issues and network reliability concerns. Organizations relying on juniper switches for critical network infrastructure face significant risk from this vulnerability, particularly in environments where dhcp services are actively utilized and where network clients may be compromised or malicious. The gradual nature of the memory exhaustion means that detection may be delayed until the system reaches critical failure points, potentially leading to extended outages. The fxpc process crash represents a complete failure of the packet forwarding engine, requiring manual intervention or automatic system restarts to restore normal operations. Network administrators must contend with the challenge of monitoring heap utilization continuously and implementing preventive measures before reaching critical thresholds. The vulnerability affects both local and relay dhcp server configurations, meaning that any switch configured to handle dhcp traffic is potentially vulnerable. This creates widespread exposure across networks where dhcp services are deployed, particularly in enterprise environments where multiple switches may be configured with dhcp relay capabilities.
Mitigation strategies for this vulnerability should focus on both immediate protective measures and long-term architectural improvements. The most effective immediate response involves implementing dhcp rate limiting or filtering mechanisms to prevent excessive dhcp packet processing that could trigger memory exhaustion. Network administrators should establish monitoring procedures to track packet dma heap utilization and implement automated alerts when utilization exceeds 80% to prevent reaching the critical 99% threshold. Configuration changes should include limiting dhcp packet processing rates and implementing proper dhcp server authentication mechanisms to prevent unauthorized or malicious dhcp traffic. The implementation of network segmentation and access control lists can help reduce exposure by limiting which clients can send dhcp packets to vulnerable switches. Organizations should also consider implementing dhcp snooping features and other network security controls that can detect and filter anomalous dhcp traffic patterns. The vulnerability aligns with common attack patterns described in the attack tree framework, particularly those involving resource exhaustion and denial of service attacks. From a compliance perspective, this vulnerability may impact various security standards including nist 800 53 and iso 27001 requirements for system availability and resilience. Organizations should also consider implementing incident response procedures specifically addressing this type of memory exhaustion attack to ensure rapid recovery and minimal business impact.