CVE-2026-102031 in Junos OS Evolved
Summary
by MITRE • 10/15/2026
An OS Command Injection vulnerability in TACACS of Juniper Networks Junos OS Evolved allows a low-privileged TACACS+-authenticated user to execute commands with root privileges when periodic TACACS+ authorization-refresh is enabled.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability represents a critical security flaw within the Terminal Access Controller Access-Control System Plus (TACACS+) implementation of Juniper Networks Junos OS Evolved, specifically affecting configurations where periodic authorization refreshes are active. This operating system serves as the foundational software for many high-performance network devices, and its authentication mechanisms are central to maintaining administrative integrity across enterprise networks. The vulnerability stems from a failure in input validation during the processing of TACACS+ authorization responses when these responses trigger automatic re-authorization events at regular intervals. Under normal operational parameters, a low-privileged user authenticates with limited permissions and expects their access rights to remain static or change only through explicit administrative action. However, due to this flaw, the system incorrectly processes specific elements within the periodic refresh packets sent by the TACACS+ server, allowing an attacker who has obtained valid credentials for a low-level account to inject operating system commands that are subsequently executed with root privileges.
From a technical perspective, this issue is classified as OS Command Injection, which corresponds directly to Common Weakness Enumeration identifier CWE-78. The core of the problem lies in how Junos OS Evolved parses and executes shell commands derived from external authentication server responses without sufficiently sanitizing special characters or controlling command execution contexts during the automated refresh cycle. When periodic authorization-refresh is enabled, the device periodically queries the TACACS+ server to update user permissions. If an attacker controls a low-privileged account on this system, they can manipulate their session state by exploiting the parsing logic used in these periodic updates. By crafting specific payloads within the context of the authentication exchange or leveraging side-channel effects during the refresh process, the attacker bypasses privilege escalation restrictions intended to isolate lower-level users from critical system functions. This effectively transforms a standard user account into a privileged shell access point without requiring password guessing or credential theft beyond initial legitimate acquisition.
The operational impact of this vulnerability is severe, as it allows for complete compromise of the network device hosting Junos OS Evolved. Once an attacker achieves root-level command execution via TACACS+ injection, they gain unrestricted control over the underlying operating system. This level of access enables the modification of firewall rules to bypass security policies, interception and manipulation of routing protocols leading to traffic redirection or denial-of-service conditions, installation of persistent backdoors for long-term unauthorized access, and exfiltration of sensitive configuration data including cryptographic keys and network topology details. Furthermore, because TACACS+ is often used as a centralized authentication source for multiple devices across an organization, compromising one device through this vector may facilitate lateral movement if shared credentials or similar configurations exist elsewhere in the infrastructure. The ability to execute commands with root privileges means that traditional perimeter defenses become irrelevant once initial access via low-privileged accounts is established and exploited.
This vulnerability aligns with several tactics within the MITRE ATT&CK framework, particularly Initial Access through Valid Accounts and Privilege Escalation techniques involving command injection. Attackers can leverage this flaw to escalate from a standard user role to full system control without triggering typical privilege escalation alerts that monitor for direct sudo or su usage patterns. The exploitation does not require network-level vulnerabilities such as buffer overflows but rather relies on logical flaws in how authentication services interact with the local shell environment during automated maintenance tasks like authorization refreshes. This makes detection more challenging, as standard intrusion prevention systems may not flag legitimate TACACS+ traffic unless specific command injection signatures are actively monitored and deployed within deep packet inspection profiles tailored for AAA protocols.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is to apply the vendor-provided software patches that address this parsing flaw in Junos OS Evolved, ensuring all devices running affected versions are updated promptly. In environments where patching cannot be immediately implemented due to operational constraints, administrators should disable periodic TACACS+ authorization-refresh features if they are not strictly required for business continuity or compliance mandates. Reducing the frequency of refreshes can also mitigate risk by limiting the window of opportunity for exploitation attempts. Additionally, implementing strict network segmentation ensures that only authorized management stations and specific authentication servers can communicate with device interfaces handling AAA traffic, thereby reducing the attack surface available to potential adversaries who might have gained foothold elsewhere in the network.
Long-term security posture improvements should include enforcing multi-factor authentication for all administrative accounts regardless of privilege level, which adds a layer of verification beyond simple password possession even if credentials are compromised. Regular auditing of TACACS+ server logs and device authorization events can help identify anomalous patterns indicative of exploitation attempts, such as unusual spikes in refresh requests or unexpected command executions logged at the root level. Adopting a principle of least privilege across all network devices ensures that even if an attacker successfully exploits this vulnerability on one system, their ability to pivot laterally is constrained by minimal permissions assigned to other accounts and services. Continuous monitoring using security information and event management solutions configured with specific rules for AAA protocol anomalies remains essential for detecting sophisticated attacks targeting authentication infrastructure components like TACACS+.