CVE-2021-31373 in Junos OS
Summary
by MITRE • 10/19/2021
A persistent Cross-Site Scripting (XSS) vulnerability in Juniper Networks Junos OS on SRX Series, J-Web interface may allow a remote authenticated user to inject persistent and malicious scripts. An attacker can exploit this vulnerability to steal sensitive data and credentials from a web administration session, or hijack another user's active session to perform administrative actions. This issue affects: Juniper Networks Junos OS on SRX Series: 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 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 20.2R3-S1; 20.3 versions prior to 20.3R2-S1, 20.3R3.
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Analysis
by VulDB Data Team • 10/27/2021
The vulnerability described in CVE-2021-31373 represents a critical persistent cross-site scripting flaw within the Juniper Networks Junos OS operating system, specifically affecting the SRX Series firewall devices through their J-Web administrative interface. This persistent XSS vulnerability arises from inadequate input validation and output encoding mechanisms within the web interface components, allowing authenticated attackers to inject malicious scripts that persistently execute within the context of other users' browser sessions. The flaw fundamentally compromises the integrity of the web-based management interface, creating a persistent threat vector that can maintain its effect across multiple user interactions and sessions.
The technical implementation of this vulnerability stems from insufficient sanitization of user-supplied input parameters within the J-Web interface of Junos OS. When authenticated users interact with specific administrative functions, the system fails to properly validate or encode input data before rendering it in web responses, creating an environment where malicious payloads can be stored and subsequently executed. This persistent nature means that the injected scripts are not merely reflected in a single request but are stored within the application's data processing mechanisms and executed whenever affected pages are accessed by other users. The vulnerability specifically impacts multiple versions of the Junos OS across different release branches, indicating a widespread issue within the software's input handling architecture.
The operational impact of this vulnerability extends beyond simple script execution, creating significant risks for administrative security and data integrity. An attacker who successfully exploits this vulnerability can hijack active user sessions, effectively gaining administrative privileges without requiring additional authentication mechanisms. This session hijacking capability allows malicious actors to perform any administrative actions available to legitimate users, potentially leading to complete system compromise, unauthorized configuration changes, data exfiltration, and the establishment of persistent backdoors. The vulnerability particularly affects environments where multiple administrators access the same management interface, as a single compromised session can provide access to all administrative functions.
Security implications of CVE-2021-31373 align with CWE-79, which categorizes cross-site scripting vulnerabilities as weaknesses in input validation and output encoding. The persistent nature of this flaw also relates to ATT&CK technique T1566, specifically focusing on the exploitation of web application vulnerabilities for initial access and privilege escalation. Organizations utilizing affected Juniper SRX Series devices face substantial risk exposure, particularly in environments where administrative access to network security devices is centralized and where multiple users share the same management interface. The vulnerability essentially undermines the trust model of the web administration interface, as any authenticated user could potentially inject malicious code that affects all other users with access to the same system.
Mitigation strategies for this vulnerability require immediate patching of affected Junos OS versions to the recommended secure releases, which include the specific service pack versions mentioned in the vulnerability description. Network administrators should implement strict access controls and monitoring of administrative sessions to detect potential exploitation attempts, while also considering network segmentation to limit access to the affected devices. Additional protective measures include implementing web application firewalls to filter malicious input, establishing robust session management policies, and conducting regular security assessments of administrative interfaces. Organizations should also review their incident response procedures to ensure readiness for potential exploitation of this vulnerability, as the persistent nature of the XSS flaw means that any successful injection can maintain its effect until the underlying vulnerability is patched and the malicious content is removed from the system's data stores.