CVE-2021-31386 in Junos OS
Summary
by MITRE • 10/19/2021
A Protection Mechanism Failure vulnerability in the J-Web HTTP service of Juniper Networks Junos OS allows a remote unauthenticated attacker to perform Person-in-the-Middle (PitM) attacks against the device. This issue affects: Juniper Networks Junos OS 12.3 versions prior to 12.3R12-S20; 15.1 versions prior to 15.1R7-S11; 18.3 versions prior to 18.3R3-S6; 18.4 versions prior to 18.4R3-S10; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R3-S4; 19.3 versions prior to 19.3R3-S4; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R3-S2; 20.2 versions prior to 20.2R3-S3; 20.3 versions prior to 20.3R3-S1; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R3; 21.2 versions prior to 21.2R2.
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Analysis
by VulDB Data Team • 10/27/2021
The vulnerability identified as CVE-2021-31386 represents a critical protection mechanism failure within the J-Web HTTP service of Juniper Networks Junos OS operating systems. This weakness fundamentally compromises the security posture of affected network devices by creating an avenue for remote attackers to execute person-in-the-middle attacks without requiring authentication credentials. The flaw resides in the implementation of secure communication protocols within the web interface service, which fails to properly validate or establish secure connections between remote clients and the network devices.
The technical nature of this vulnerability stems from insufficient cryptographic protection mechanisms within the J-Web service, specifically affecting the TLS/SSL handshake process and certificate validation procedures. Attackers can exploit this weakness to intercept and potentially modify communications between administrators and network devices, effectively undermining the integrity and confidentiality of management sessions. The vulnerability affects multiple major release branches of Junos OS, spanning from version 12.3 through 21.2, indicating a long-standing issue that persisted across numerous software versions and maintenance releases.
From an operational impact perspective, this vulnerability creates significant risk for network infrastructure security, particularly in environments where Juniper devices serve as critical network components. The ability to perform man-in-the-middle attacks against network management interfaces enables attackers to gain unauthorized access to device configurations, execute administrative commands, and potentially escalate privileges within the network. The remote unauthenticated nature of the attack means that adversaries can exploit this weakness from anywhere on the internet without requiring prior access credentials or physical presence at the network site.
Organizations affected by CVE-2021-31386 face substantial security implications including potential data breaches, unauthorized network access, and compromise of critical infrastructure. The vulnerability aligns with CWE-310 (Cryptographic Issues) and maps to ATT&CK technique T1071.004 (Application Layer Protocol: DNS) and T1566 (Phishing) within the enterprise attack framework, as it enables attackers to establish malicious communication channels that could facilitate further exploitation. Network defenders must consider this vulnerability as part of a broader threat landscape where compromised management interfaces can lead to complete network compromise.
The recommended mitigation strategy involves immediate deployment of software patches and updates provided by Juniper Networks to address the cryptographic weakness in the J-Web service. Organizations should also implement network segmentation and monitoring controls to detect anomalous communication patterns that might indicate exploitation attempts. Additional protective measures include disabling unnecessary web management services, implementing strong access controls, and conducting comprehensive network audits to identify and remediate similar vulnerabilities across the infrastructure. The vulnerability demonstrates the critical importance of maintaining up-to-date security patches and implementing robust cryptographic practices in network management interfaces as outlined in industry standards including NIST SP 800-53 and ISO/IEC 27001 security controls.