CVE-2022-22180 in Junos OS
Summary
by MITRE • 01/19/2022
An Improper Check for Unusual or Exceptional Conditions vulnerability in the processing of specific IPv6 packets on certain EX Series devices 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 a crash of the fxpc process. An indication of the issue occurring may be observed through the following log messages: Sep 13 17:14:59 hostname : %PFE-3: fpc0 (buf alloc) failed allocating packet buffer Sep 13 17:14:59 hostname : %PFE-7: fpc0 brcm_pkt_buf_alloc:393 (buf alloc) failed allocating packet buffer When Packet DMA heap utilization reaches 99%, the system will become unstable. Packet DMA heap utilization can be monitored using the 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 • 01/20/2022
This vulnerability represents a critical improper check for unusual or exceptional conditions within the IPv6 packet processing pipeline of juniper ex series network devices. The flaw manifests when specific IPv6 packets are processed, triggering an abnormal memory allocation pattern that leads to exhaustion of the DMA (Direct Memory Access) memory pool. According to the cwe-252 standard, this vulnerability stems from inadequate validation of exceptional conditions during packet handling operations, specifically failing to properly manage memory allocation failures that occur during packet buffer allocation. The issue directly impacts the forwarding plane functionality of these network devices, creating a scenario where normal traffic processing becomes impossible due to resource exhaustion.
The technical implementation of this vulnerability involves the failure to properly handle packet buffer allocation requests within the fpc (forwarding processor card) environment. When the system encounters specific IPv6 packet structures, it attempts to allocate packet buffers from the DMA heap memory space without sufficient error handling or resource management checks. The log messages indicate that the system fails at the fpc0 level where buffer allocation operations consistently fail, demonstrating that the underlying memory management subsystem cannot properly handle these exceptional packet conditions. This failure mode aligns with the att&ck technique t1499.004 which involves network denial of service through resource exhaustion attacks. The vulnerability operates at the packet processing level, where the system's inability to gracefully handle exceptional packet structures results in progressive memory consumption until the DMA heap reaches critical utilization levels.
The operational impact of this vulnerability extends beyond simple service interruption to potentially causing complete system instability and crash conditions. As demonstrated by the heap utilization statistics showing 99% usage of the Packet DMA memory pool, the system becomes increasingly unstable as memory resources dwindle. The fxpc process crash represents the most severe outcome, as this process is critical to the forwarding functionality of the device. The gradual nature of the memory exhaustion means that administrators may observe increasing instability over time before complete system failure occurs, making early detection challenging. Network administrators monitoring these systems will notice the characteristic log messages indicating buffer allocation failures, which serve as early warning signs of the impending resource exhaustion that ultimately leads to denial of service conditions. This vulnerability directly impacts the availability and reliability of network services, particularly in environments where continuous packet forwarding is critical.
Mitigation strategies for this vulnerability should focus on both immediate operational responses and long-term architectural improvements. The recommended immediate action involves monitoring the DMA heap utilization levels and implementing automated alerts when utilization reaches critical thresholds, typically before the 99% mark. System administrators should also implement periodic restart procedures for affected fpc cards to reset memory allocation states and prevent progressive resource exhaustion. Network segmentation and traffic filtering can help reduce the likelihood of exploitation by limiting the types of IPv6 packets that reach vulnerable systems. Additionally, implementing proper input validation and error handling mechanisms within the packet processing pipeline would address the root cause by ensuring that exceptional packet conditions are properly managed rather than allowing them to consume system resources. The fix should include implementing proper resource cleanup procedures and robust error handling that prevents allocation failures from causing progressive memory consumption, aligning with security best practices for maintaining system stability under exceptional conditions.