Description

An Improper Authentication vulnerability in J-Web of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated network attacker to bypass J-Web authentication and execute CGI content with elevated privileges via a crafted HTTP request.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-10-14T17:17:50.953Z",
  "pubdate": "2026-10-14T17:17:50.953Z",
  "executiveSummary": "This vulnerability involves an Improper Authentication flaw within the J-Web management interface of Juniper Networks Junos OS and Junos OS Evolved.\nThe vulnerability allows an unauthenticated, remote network attacker to bypass existing authentication mechanisms, leading to unauthorized execution of Common Gateway Interface (CGI) content.\nBy successfully exploiting this flaw, an attacker can execute commands or scripts with elevated privileges, effectively compromising the integrity and availability of the affected device.\nThe risk is critical, as it requires no prior authentication or user interaction to facilitate exploitation, providing a direct vector for remote code execution.\nAffected systems are those running J-Web, which serves as the web-based graphical user interface for managing Juniper network hardware.\nThe primary security implication is complete administrative control over the management plane of the device, potentially allowing for configuration changes, persistent backdoor installation, or lateral movement within the network.",
  "technicalDetails": "The vulnerability exists within the J-Web component, which handles web-based administrative requests for Junos OS and Junos OS Evolved. The root cause is an Improper Authentication flaw in the request processing logic, which fails to correctly validate the authenticity of incoming HTTP requests before invoking CGI programs.\nThe attack vector involves a crafted HTTP request sent to the J-Web interface. Because the vulnerability resides in the authentication handshake or the authorization verification phase of the CGI handler, an attacker can bypass the intended access control checks. By manipulating specific HTTP headers or request parameters, the attacker tricks the application into treating a non-authenticated request as an authorized administrative session.\nThe exploitation flow proceeds as follows: First, the attacker identifies a target device with J-Web enabled and exposed to the network. Second, the attacker constructs a specialized HTTP request that targets specific CGI endpoints. Third, the J-Web server fails to enforce the required authentication handshake, incorrectly concluding that the request is legitimate. Fourth, the server executes the targeted CGI content using elevated privileges associated with the J-Web service process.\nBecause the CGI process runs with elevated system privileges, the attacker can leverage this execution to perform unauthorized actions, including the reading or modification of sensitive configuration files, retrieval of system credentials, or execution of arbitrary shell commands. This effectively grants the attacker administrative-level control over the Junos OS environment without having any valid credentials.\nThe vulnerability is restricted to the J-Web management component; however, since this service is typically exposed to internal or external network segments for administrative access, the network exposure is significant. There are no prerequisite privilege requirements for the attacker, as the vulnerability explicitly bypasses these constraints. The post-exploitation impact includes full system compromise, the potential for traffic interception, and the ability to pivot into protected segments of the network infrastructure managed by the affected device."
}