CVE-2021-31377 in Junos OS
Summary
by MITRE • 10/19/2021
An Incorrect Permission Assignment for Critical Resource vulnerability of a certain file in the filesystem of Junos OS allows a local authenticated attacker to cause routing process daemon (RPD) to crash and restart, causing a Denial of Service (DoS). Repeated actions by the attacker will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S7; 19.1 versions prior to 19.1R2-S3, 19.1R3-S5; 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-S2; 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 20.3R3; 20.4 versions prior to 20.4R1-S1, 20.4R2.
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Analysis
by VulDB Data Team • 10/27/2021
The vulnerability identified as CVE-2021-31377 represents a critical incorrect permission assignment flaw within Junos OS that directly impacts the routing process daemon (RPD) functionality. This issue stems from improper file system permissions that allow local authenticated attackers to manipulate critical system resources, ultimately leading to service disruption through daemon crashes and restarts. The vulnerability specifically targets the routing process daemon which is fundamental to network packet forwarding and routing table maintenance across juniper network devices. The flaw manifests when an authenticated user with limited privileges can exploit misconfigured file permissions to trigger a crash condition in the RPD process, which then automatically restarts the daemon service. This behavior creates a cascading effect where repeated exploitation attempts can maintain sustained denial of service conditions, effectively compromising network availability and operational continuity.
The technical implementation of this vulnerability aligns with CWE-732, which describes Incorrect Permission Assignment for Critical Resource, a classification that specifically addresses scenarios where system resources receive inappropriate access controls. The attack vector requires local authentication since the vulnerability exploits file system permissions that are accessible to authenticated users but should be restricted to privileged system processes. The affected Junos OS versions span multiple major releases including 15.1, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, and 20.4, indicating a widespread impact across the Juniper networking platform. The specific versions requiring patches show a pattern where security fixes were implemented in subsequent service releases, with each major version receiving multiple patch releases addressing different aspects of the vulnerability. This widespread exposure demonstrates the critical nature of the permission misconfiguration that allowed attackers to manipulate core routing functionality through seemingly benign file system access controls.
From an operational impact perspective, this vulnerability enables attackers to achieve sustained denial of service conditions that can severely disrupt network operations and compromise service availability. The routing process daemon crash and restart cycle creates a persistent threat that can degrade network performance, interrupt data transmission, and potentially cause cascading failures in larger network infrastructures where routing stability is critical. The sustained nature of the DoS condition means that network administrators must continuously monitor for exploitation attempts and maintain active patch management protocols to prevent service disruption. The vulnerability particularly affects network infrastructure devices where routing stability is paramount, as any disruption to RPD functionality can cause complete routing table inconsistencies and packet forwarding failures across affected network segments. Network operators face the challenge of identifying and remediating this vulnerability across multiple device generations and software versions, requiring coordinated patch deployment strategies to maintain network security and operational integrity.
The mitigation strategy for CVE-2021-31377 requires immediate implementation of the official Juniper security patches that address the incorrect permission assignment for critical resources. Network administrators should prioritize patch deployment across all affected Junos OS versions, particularly focusing on the service release versions that contain the specific fixes for this vulnerability. The ATT&CK framework classification for this vulnerability would align with T1499.004, which covers network disruption through service availability, and T1068, which addresses local privilege escalation through improper access control. Organizations should implement comprehensive monitoring solutions to detect unauthorized access attempts and anomalous behavior patterns that may indicate exploitation attempts. Network segmentation strategies should be reinforced to limit local access privileges and reduce the attack surface available to authenticated users. Additionally, implementing proper file system permission auditing and regular security assessments can help identify similar misconfigurations that could potentially expose other critical system resources to unauthorized manipulation. The vulnerability serves as a reminder of the importance of maintaining proper access controls and privilege separation in network infrastructure systems to prevent authenticated users from exploiting permission misconfigurations to cause service disruption.