CVE-2026-102055 in Junos OS
Summary
by MITRE • 10/14/2026
A Stack-based Buffer Overflow vulnerability in the cfmd process of Juniper Networks Junos OS on MX Series and Junos OS Evolved on PTX Series platforms allows an unauthenticated adjacent-network attacker to execute arbitrary code as root or cause denial of service via a specific CFM Message sent to a configured down-MEP with enhanced CFM mode enabled.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified in the Cisco Framework Maintenance daemon, known as cfmd, within Juniper Networks Junos OS and Junos OS Evolved represents a critical security flaw rooted in improper memory management during packet processing. This stack-based buffer overflow occurs specifically when the system processes Control Plane Integrity (CFM) messages directed at configured maintenance end points with enhanced CFM mode enabled. The architecture of cfmd, which is responsible for handling connectivity fault management protocols essential for network monitoring and diagnostics, fails to adequately validate the length or structure of incoming CFM packets before copying them into a fixed-size stack buffer. This lack of rigorous input validation allows an attacker who has crafted a maliciously sized CFM message to overwrite adjacent memory locations on the call stack, thereby gaining control over critical execution context data such as return addresses and saved frame pointers.
From an operational perspective, this flaw poses severe risks due to its accessibility by unauthenticated attackers located on the same network segment. Because connectivity fault management protocols are often exposed within local area networks for troubleshooting purposes, any device connected to the affected MX Series or PTX Series platforms can attempt exploitation without requiring prior authentication credentials. The impact of successful exploitation is twofold: an attacker may achieve arbitrary code execution with root privileges, effectively compromising the integrity and confidentiality of the entire network infrastructure by gaining full control over the routing engine. Alternatively, if the exploit fails to establish persistent access or triggers a crash condition during memory corruption, it results in a denial of service that disrupts critical network monitoring functions, potentially masking other malicious activities or causing significant operational downtime for enterprise networks relying on these platforms for high availability and fault detection.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-121, which describes stack-based buffer overflow conditions resulting from insufficient bounds checking during data copying operations. Furthermore, the exploitation technique maps to MITRE ATT&CK techniques associated with initial access via network service vulnerabilities and privilege escalation through local exploits. The ability of an adjacent attacker to trigger this condition highlights a gap in perimeter defense strategies that assume internal networks are trusted environments without implementing strict protocol validation at the application layer. Such oversights allow lateral movement within the network segment, enabling attackers to pivot from simple reconnaissance or denial-of-service attacks to full system compromise.
Mitigation requires immediate attention to patch management and configuration hardening practices. Juniper Networks has released software updates that address this issue by implementing stricter input validation mechanisms within the cfmd process to ensure that CFM message lengths do not exceed allocated buffer sizes before processing occurs. Administrators should apply these patches promptly to all affected MX Series and PTX Series platforms running vulnerable versions of Junos OS or Junos OS Evolved. In addition to software updates, network segmentation strategies can reduce exposure by restricting access to management interfaces and diagnostic protocols from untrusted zones. Implementing strict firewall rules that limit CFM traffic to authorized monitoring stations only adds a layer of defense-in-depth, reducing the attack surface available to adjacent-network adversaries attempting to exploit this stack-based buffer overflow vulnerability.