The vulnerability CVE-2025-21590 is a local privilege escalation vulnerability in Juniper Networks Junos OS, resulting from insufficient process isolation and improper privilege management within the kernel. The flaw allows a local attacker with high privileges and shell access to inject and execute arbitrary code. Due to inadequate sandboxing mechanisms, privileged users can manipulate system parameters to load malicious code, leading to unauthorized system modifications. The vulnerability is particularly dangerous because it enables attackers to escalate privileges, execute arbitrary commands, or install persistent backdoors, ultimately compromising the affected device.

Exploitation requires local shell access, which could be obtained through stolen credentials, insider threats, or leveraging another exploit. Attackers can inject malicious code into system processes by exploiting weak process isolation and improper handling of user-controlled data. Once executed, this payload enables them to gain root-level access, tamper with system configurations, and potentially load malicious kernel modules for further exploitation. While the attack cannot be initiated through the Junos Command Line Interface (CLI), it poses a significant risk to environments where shell access is exposed.