CVE-2021-31369 in Junos OS
Summary
by MITRE • 10/19/2021
On MX Series platforms with MS-MPC/MS-MIC, an Allocation of Resources Without Limits or Throttling vulnerability in Juniper Networks Junos OS allows an unauthenticated network attacker to cause a partial Denial of Service (DoS) with a high rate of specific traffic. If a Class of Service (CoS) rule is attached to the service-set and a high rate of specific traffic is processed by this service-set, for some of the other traffic which has services applied and is being processed by this MS-MPC/MS-MIC drops will be observed. Continued receipted of this high rate of specific traffic will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on MX Series with MS-MPC/MS-MIC: All versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S7, 19.3R3-S3; 19.4 versions prior to 19.4R3-S5; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2.
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Analysis
by VulDB Data Team • 10/23/2021
This vulnerability represents a critical resource allocation flaw within Juniper Networks Junos OS operating on MX Series platforms equipped with MS-MPC/MS-MIC hardware components. The issue manifests as an improper handling of traffic processing within Class of Service (CoS) rules that are attached to service-sets, creating a scenario where unauthenticated network attackers can exploit this weakness to induce partial denial of service conditions. The vulnerability specifically targets the memory and processing resource management mechanisms within the hardware-based packet processing units, where insufficient limits or throttling controls allow malicious traffic patterns to overwhelm the system's ability to handle legitimate traffic streams effectively. The flaw operates at the intersection of network traffic processing and resource management, creating a pathway for attackers to disrupt normal network operations through carefully crafted traffic volumes.
The technical implementation of this vulnerability stems from inadequate resource allocation controls within the CoS processing pipeline of the MS-MPC/MS-MIC hardware modules. When specific traffic patterns exceed predetermined thresholds within the service-set processing framework, the system fails to properly throttle or limit resource consumption, resulting in observed packet drops for other legitimate traffic streams that share the same processing resources. This behavior creates a cascading effect where sustained high-rate traffic can maintain a persistent denial of service condition, as the system's resource management mechanisms cannot adequately distinguish between different traffic types or maintain appropriate resource boundaries. The vulnerability is particularly dangerous because it operates at the hardware level within the MS-MPC/MS-MIC modules, making it difficult to detect and mitigate through traditional software-based approaches.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network reliability and availability for extended periods. Network administrators may observe intermittent packet loss, reduced throughput, or complete service unavailability for traffic streams that share the affected processing resources. The sustained nature of the DoS condition means that once an attacker begins sending the specific traffic patterns, the system may remain in a degraded state until manual intervention occurs or the system is rebooted. This vulnerability affects multiple Junos OS versions across several release branches, indicating a widespread issue that has persisted through various software iterations, suggesting that the root cause lies within fundamental architectural design decisions rather than isolated coding errors.
Mitigation strategies should focus on implementing immediate software patches and updates to affected Junos OS versions, while also considering network-level controls such as traffic rate limiting and access control lists to prevent exploitation. The vulnerability aligns with CWE-770, which addresses allocation of resources without limits or throttling, and demonstrates characteristics consistent with ATT&CK technique T1498, which involves denial of service attacks. Organizations should prioritize updating to patched versions of Junos OS, particularly those mentioned in the advisory, while implementing network monitoring to detect anomalous traffic patterns that might indicate exploitation attempts. Additionally, network segmentation and traffic classification controls can help limit the scope of potential impact, though the hardware-level nature of the vulnerability makes complete protection challenging without proper software patches.