CVE-2026-102049 in Junos OS
Summary
by MITRE • 10/14/2026
A Stack-based Buffer Overflow vulnerability in the l2cpd process of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent unauthenticated attacker to cause a denial of service or execute arbitrary code with root privileges via LLDP traffic received on an interface with Unified Access Policy enabled.
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Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability represents a critical security flaw within the Layer 2 Control Protocol daemon, known as l2cpd, which is a core component of Juniper Networks Junos OS and Junos OS Evolved operating systems. This specific weakness manifests as a stack-based buffer overflow, a classic memory corruption error where data written to a buffer exceeds its allocated boundary on the call stack. The vulnerability can be triggered by an adjacent unauthenticated attacker who sends crafted Link Layer Discovery Protocol traffic to any network interface that has Unified Access Policy enabled. Because LLDP is typically used for device discovery and configuration management in local area networks, it operates at layer two of the OSI model, allowing attackers with physical or logical access to the same broadcast domain to exploit this flaw without needing valid credentials.
The technical root cause lies in insufficient bounds checking within the l2cpd process when parsing incoming LLDP packets. When a maliciously crafted packet is received, specifically one containing oversized fields or malformed TLVs (Type-Length-Value structures), the application fails to validate the input length against the fixed-size buffer allocated on the stack. This allows an attacker to overwrite adjacent memory locations, including return addresses and function pointers stored on the stack frame. By carefully crafting the payload, an attacker can manipulate these overwritten values to redirect program execution flow. Given that l2cpd typically runs with elevated privileges to manage network interfaces and control plane protocols, successful exploitation results in arbitrary code execution with root-level access rights.
The operational impact of this vulnerability is severe, encompassing both denial of service and full system compromise. In the case of a denial of service attack, an attacker can send malformed LLDP packets that cause the l2cpd process to crash or hang due to memory corruption errors such as segmentation faults. Since l2cpd handles critical Layer 2 control functions, its failure can disrupt network connectivity, prevent device discovery, and potentially affect other services dependent on stable layer two operations. More critically, if the attacker achieves code execution, they gain complete control over the affected device. This allows for further lateral movement within the network, installation of persistent backdoors, exfiltration of sensitive data, or use of the compromised router as a pivot point for attacks against internal infrastructure. The requirement for Unified Access Policy to be enabled narrows the attack surface slightly but does not eliminate the risk for organizations utilizing this security feature set.
From an industry standard perspective, this vulnerability aligns with CWE-120: Buffer Copy without Checking Size of Input, which describes the failure to validate input length before copying it into a buffer. Additionally, the exploitation technique falls under MITRE ATT&CK tactic Tactic 6: Defense Evasion and Technique T1548: Abuse Configuration or Settings, as well as potential privilege escalation paths associated with CWE-269: Improper Privilege Management. The ability to execute code remotely via network traffic places this in the context of remote code execution vulnerabilities often seen in network device firmware.
Mitigation strategies should prioritize immediate patching by applying the latest software updates provided by Juniper Networks, which address the buffer validation logic within l2cpd. In environments where patches cannot be applied immediately, administrators should consider disabling LLDP on interfaces that do not require it for operational purposes, thereby reducing the attack surface. Furthermore, implementing strict access control lists to restrict LLDP traffic to trusted management networks can provide an additional layer of defense. Network segmentation is also recommended to isolate critical infrastructure from untrusted zones, ensuring that even if a device in a less secure segment is compromised, the attacker cannot easily reach devices with Unified Access Policy enabled or other high-value targets on the core network. Regular vulnerability scanning and monitoring for anomalous LLDP traffic patterns can aid in early detection of exploitation attempts.