The vulnerability is an improper authentication flaw in the J‑Web interface that allows an unauthenticated network attacker to forge a special HTTP request and bypass the normal login mechanism. Once authentication is bypassed, the attacker can execute CGI scripts with elevated system privileges. This enables remote code execution, allowing an attacker to run arbitrary commands on the device, which could compromise the confidentiality, integrity, and availability of the network infrastructure.

The flaw affects Juniper Networks Junos OS and Junos OS Evolved. All Junos OS releases up to the listed fixed versions are vulnerable, including 23.2R2‑S7.7, 23.4R2‑S8.13, 24.2R2‑S5.5, 24.4R2‑S5, 25.2R2‑S2, 25.4R1‑S3, 25.4R2, 26.2R, 26.2R2, 26.4R1 and every subsequent Junos OS release. For Junos OS Evolved, the vulnerable releases include 23.2R2‑S7.7‑EVO, 23.4R2‑S8.11‑EVO, 24.2R2‑S5.6‑EVO, 24.4R2‑S5‑EVO, 25.2R2‑S2‑EVO, 25.2X100‑D35‑EVO, 25.4R1‑S3‑EVO, 25.4R2‑EVO, 25.4X300‑D40‑EVO, 26.2R1‑S2‑EVO, 26.2R2‑EVO, 26.4R1‑EVO and any subsequent Junos OS Evolved release. Specific respins of these major releases were also referenced as part of the fix.

The CVSS score of 9.3 classifies the vulnerability as critical, indicating a high potential impact. The EPSS score of 0.00578 indicates a very low but non‑zero probability of exploitation; however, the lack of a workaround and the absence from the KEV catalog suggest that the flaw may be exploited by targeted adversaries. Attackers can exploit the issue remotely by sending a crafted HTTP request to the J‑Web service from outside the network, gaining elevated privileges without prior authentication. Access to the device’s J‑Web port enables this attack vector, making it a highly actionable threat for external attackers.