CVE-2021-31383 in Junos OS
Summary
by MITRE • 10/19/2021
In Point to MultiPoint (P2MP) scenarios within established sessions between network or adjacent neighbors the improper use of a source to destination copy write operation combined with a Stack-based Buffer Overflow on certain specific packets processed by the routing protocol daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved sent by a remote unauthenticated network attacker causes the RPD to crash causing a Denial of Service (DoS). Continued receipt and processing of these packets will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS 19.2 versions prior to 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R2-S3, 20.2R3; 20.3 versions prior to 20.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R1. Juniper Networks Junos OS Evolved 20.1 versions prior to 20.1R3-EVO; 20.2 versions prior to 20.2R3-EVO; 20.3 versions prior to 20.3R2-EVO.
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Analysis
by VulDB Data Team • 10/23/2021
This vulnerability represents a critical stack-based buffer overflow within the routing protocol daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved operating systems. The flaw manifests specifically in Point to MultiPoint (P2MP) routing scenarios where established sessions exist between network neighbors, making it particularly dangerous in environments where routing protocols are actively processing traffic. The vulnerability stems from an improper source-to-destination copy write operation that fails to properly validate buffer boundaries, allowing an attacker to craft malicious packets that exceed allocated memory space. This issue affects multiple major release versions including 19.2, 19.3, 19.4, 20.1, 20.2, and 20.3, with specific patch releases required to remediate the vulnerability across each affected series. The attack vector requires a remote unauthenticated network attacker capable of sending specific packets to the affected system, which makes this vulnerability particularly concerning for publicly accessible network infrastructure. According to CWE standards, this vulnerability maps to CWE-121 Stack-based Buffer Overflow, which is classified as a high-severity weakness in the Common Weakness Enumeration catalog. The ATT&CK framework categorizes this as a Denial of Service attack technique, specifically targeting system availability through process termination or resource exhaustion.
The operational impact of CVE-2021-31383 extends beyond simple service disruption to potentially compromise entire network routing functions within affected Juniper devices. When exploited, the buffer overflow causes the RPD process to crash, which results in immediate denial of service conditions that can persist until manual intervention occurs or the device is rebooted. The sustained nature of this vulnerability means that continued receipt of malicious packets maintains the DoS condition, effectively creating a persistent availability threat that can last until the vulnerable system is patched or restarted. Network administrators face significant operational challenges as this vulnerability can affect routing stability across entire network segments, particularly in environments where P2MP scenarios are common such as in MPLS networks, multicast routing deployments, or any environment utilizing Juniper's routing protocols. The vulnerability affects both traditional Junos OS and the newer Junos OS Evolved platform, indicating a fundamental flaw in the routing protocol daemon implementation that spans multiple Juniper OS variants.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Juniper Networks, with specific release versions recommended for each affected series. Organizations should prioritize patching devices running affected Junos OS versions, particularly those in critical network paths where routing stability is essential. Network segmentation and access control measures can provide temporary protection by limiting network access to only trusted sources, though this approach does not eliminate the vulnerability itself. Monitoring for suspicious packet patterns and implementing intrusion detection systems can help identify exploitation attempts, though the vulnerability's nature as an unauthenticated remote attack makes such detection challenging. Juniper has provided specific patch releases for each affected version series, including 19.2R3-S2, 19.3R2-S6, 19.4R1-S4, 20.1R2-S2, 20.2R2-S3, and 20.3R2, with corresponding releases for the Junos OS Evolved platform. Security teams should also consider implementing rate limiting on routing protocol traffic and configuring logging to capture and analyze packet patterns that might indicate exploitation attempts. The vulnerability's impact on routing protocols makes it particularly dangerous in enterprise and service provider environments where network availability is paramount, requiring immediate attention from security operations teams to prevent potential widespread network disruption.