CVE-2026-76866 in NR255-V
Summary
by MITRE • 09/16/2026
Netcore NR255-V firmware version 1.5.130703 builds root-run command lines from unquoted user-supplied DDNS input in DDNSset_cgi.c and related ddns_Proc.c components, enabling os command argument injection. Attackers can exploit the unsanitized parameters to inject additional command arguments executed with root privileges.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in Netcore NR255-V firmware version 1.5.130703 represents a critical security flaw rooted in improper input validation and shell metacharacter handling within the Dynamic DNS configuration components. Specifically, the defect resides in the DDNSset_cgi.c module and related processing logic found in ddns_Proc.c. These modules are responsible for accepting user-supplied Domain Name System (DNS) update parameters to configure dynamic IP address resolution services on the router. The core technical failure occurs when these unquoted inputs are directly concatenated into operating system command strings that are subsequently executed with root privileges via a shell interpreter such as sh or bash. This architectural decision bypasses standard parameterization safeguards, creating a direct pathway for OS Command Argument Injection.
From a technical perspective, this flaw is classified under CWE-78 Improper Neutralization of Special Elements used in an Operating System Command Shell and more specifically aligns with CWE-88 Action on Data with Incorrect Syntax leading to 'Argument Injection'. The vulnerability exploits the shell's ability to interpret special characters like spaces, semicolons, ampersands, and pipes as command delimiters or logical operators. When a user provides a DDNS hostname that includes these metacharacters without proper quoting or escaping mechanisms in the source code, the resulting system call does not treat the input as a single string argument. Instead, the shell parses the injected characters as separate commands or arguments appended to the intended command line. This allows an attacker to append arbitrary operating system commands to the legitimate DDNS update process.
The operational impact of this vulnerability is severe due to the privilege level at which the affected code executes. Because the vulnerable functions run with root privileges, any successfully injected command inherits these elevated permissions. An authenticated local attacker or a remote attacker who can trigger the CGI endpoint without authentication could execute arbitrary system commands on the device. This capability effectively results in complete compromise of the router's operating environment. The attacker can modify network configurations, install persistent backdoors, exfiltrate sensitive data such as Wi-Fi credentials and connected client information, or use the compromised device as a pivot point for further attacks against internal network resources. In many IoT deployments, this level of access also facilitates participation in botnet activities due to the widespread deployment of these devices.
This vulnerability maps directly to MITRE ATT&CK techniques related to Command and Scripting Interpreter abuse. Specifically, it aligns with T1059.004 Unix Shell commands, where attackers leverage shell metacharacters to execute additional instructions beyond those intended by the application logic. The exploitation vector typically involves crafting a malicious HTTP request containing specially formatted DDNS parameters that include command separators and payload strings. Upon processing, these inputs are passed directly to the system() or popen() functions without sanitization, leading to unintended code execution.
Mitigation strategies must address both immediate remediation and long-term secure development practices. The primary mitigation is a firmware update provided by Netcore that patches the DDNSset_cgi.c and ddns_Proc.c modules to properly quote user-supplied inputs before passing them to system commands. Developers should implement strict input validation, ensuring that only expected alphanumeric characters and standard DNS naming conventions are accepted for hostname fields. Furthermore, adopting parameterized command execution methods or avoiding shell interpreters entirely by using direct API calls instead of spawning shells can eliminate this class of vulnerability. For organizations currently operating vulnerable devices, network segmentation is recommended to limit the blast radius in case of exploitation, restricting access to the management interfaces and monitoring for anomalous outbound traffic indicative of botnet activity.