CVE-2026-57054 in Junos OS
Summary
by MITRE • 07/10/2026
A Use of Incorrectly-Resolved Name or Reference vulnerability in the URL filtering plugin of Juniper Networks Junos OS on MX Series allows an unauthenticated, network-based attacker to bypass web filtering and access downstream resources that should be unreachable.
If an MX Series device is configured with web filtering, and an attacker sends a request with a specifically formatted URL, this request will get forwarded despite the system being configured to block it. In turn, an attacker can access downstream resources that are expected to be unreachable.
This issue affects Junos OS on MX Series:
* all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S8, * 24.2 versions before 24.2R2-S5, * 24.4 versions before 24.4R2-S4, * 25.2 versions before 25.2R2-S1, * 25.4 versions before 25.4R1-S2, 25.4R2.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability represents a critical use of incorrectly-resolved name or reference flaw that undermines the fundamental security controls of web filtering systems within Juniper Networks Junos OS deployments. The issue manifests in the URL filtering plugin component of MX Series devices where improperly resolved domain names or references allow malicious requests to bypass configured access restrictions. This weakness enables attackers to circumvent network-based security policies that should prevent access to specific downstream resources, creating a significant pathway for unauthorized network traversal and information disclosure.
The technical mechanism behind this vulnerability involves the incorrect resolution of Uniform Resource Locators during the web filtering process. When an MX Series device processes incoming requests through its configured web filtering rules, the system fails to properly validate or resolve certain URL formats, allowing specifically crafted malicious requests to pass through the filtering layer without proper inspection. This misconfiguration stems from inadequate input validation and resolution handling within the URL parsing subsystem that governs how domain names and resource paths are processed before access control decisions are made.
The operational impact of this vulnerability extends beyond simple bypass of web filters to potentially expose entire downstream network segments that should remain isolated from external or unauthorized access. Attackers can exploit this weakness to gain access to internal resources, sensitive data repositories, and critical infrastructure components that are normally protected by the device's web filtering policies. The vulnerability affects multiple version streams of Juniper's operating system, indicating a widespread issue that has persisted across several release cycles, suggesting either incomplete remediation efforts or fundamental design flaws in the URL resolution mechanisms.
Network security professionals must recognize this vulnerability as a prime example of how insufficient input validation can create dangerous bypass paths within network filtering systems. The attack vector requires minimal privileges and can be executed over standard network protocols, making it particularly concerning for enterprise environments where MX Series devices serve as critical gateways for controlling internet access. This flaw directly impacts the principle of least privilege and can enable lateral movement attacks that would otherwise be blocked by properly functioning web filtering controls.
Organizations should implement immediate mitigations including deployment of patched firmware versions across all affected MX Series devices, along with enhanced monitoring for suspicious network traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-20 standards for improper input validation and relates to ATT&CK techniques involving network boundary bypass and privilege escalation through policy enforcement failures. Regular security assessments should verify proper URL resolution handling and ensure that all web filtering configurations function as intended without creating unintended access pathways. Additionally, implementing additional layers of network segmentation and access control can provide defense-in-depth measures against exploitation attempts targeting this specific vulnerability class.