CVE-2026-76861 in NR255-V
Summary
by MITRE • 09/16/2026
Netcore NR255-V version 1.5.130703 contains a stack-based buffer overflow in ntools_tcpdump_start_set.cgi caused by an unsized sprintf call when processing form values. An attacker can submit crafted input to this cgi endpoint to overflow the stack buffer and potentially execute arbitrary code.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in Netcore NR255-V version 1.5.130703 represents a critical security flaw rooted in improper memory management within the device's web interface components. Specifically, the defect resides in the ntools_tcpdump_start_set.cgi script, which is responsible for handling network diagnostic configurations submitted by users through the administrative console. This component processes form values to configure packet capture parameters, but fails to implement adequate bounds checking on input data before writing it into a fixed-size stack buffer. The core technical issue stems from an unsized sprintf call, a C standard library function that writes formatted output to a string without verifying whether the destination buffer has sufficient space to accommodate the resulting data. When an attacker submits crafted input containing characters or strings exceeding the allocated buffer size, the excess data overflows into adjacent memory locations on the stack. This overflow corrupts critical control structures such as return addresses and saved frame pointers, which are essential for maintaining the integrity of function execution flow during runtime operations.
From a technical perspective, this flaw aligns with CWE-121, Stack-based Buffer Overflow, where software writes data past the end or beginning of a fixed-size stack buffer due to insufficient validation of input length. The exploitation mechanism relies on the attacker's ability to control the content and size of the form fields processed by the CGI script. By carefully crafting payload strings that include shellcode or instructions designed to redirect execution flow, an adversary can hijack the program counter. Once the overflowed data overwrites the return address with a pointer to the injected malicious code, subsequent function returns will execute this arbitrary code within the context of the compromised process. Given that network diagnostic tools often run with elevated privileges on embedded devices like routers and gateways, successful exploitation typically results in full system compromise rather than limited local impact.
The operational impact of this vulnerability is severe, as it allows for remote code execution without authentication if the CGI endpoint is accessible to unauthenticated users or if session validation mechanisms are bypassed through additional attack vectors common in embedded web interfaces. An attacker leveraging this flaw can gain complete control over the Netcore NR255-V device, enabling them to intercept network traffic, modify routing tables, install persistent backdoors, or use the compromised device as a pivot point for further attacks against internal networks. This significantly undermines the confidentiality, integrity, and availability of services provided by the device. The presence of such vulnerabilities in consumer-grade networking hardware poses substantial risks to end-users who may lack the technical expertise to monitor system logs or apply immediate patches, leaving their home or small business networks exposed to persistent threats.
Mitigation strategies must focus on both immediate remediation and long-term secure development practices. For administrators currently running version 1.5.130703 of the Netcore NR255-V firmware, the primary defense is to upgrade to a patched version where this vulnerability has been resolved by the vendor through proper input validation and buffer size checks before performing string operations. If an update is not immediately available, restricting access to the administrative interface via IP whitelisting or disabling remote management features can reduce the attack surface. From a development standpoint, engineers should replace unsafe functions like sprintf with safer alternatives such as snprintf that enforce length limits on output strings. Additionally implementing strict input sanitization and validating all form parameters against expected formats and maximum lengths are essential steps to prevent buffer overflows. Adhering to secure coding guidelines referenced in standards like CWE-120 ensures that memory handling operations do not exceed allocated boundaries, thereby eliminating the root cause of such exploitable conditions.
This vulnerability also maps to MITRE ATT&CK techniques related to initial access and execution on compromised hosts. Specifically, it facilitates exploitation via web services where attackers leverage application-layer vulnerabilities to execute arbitrary commands. Understanding this mapping helps security teams prioritize detection rules in intrusion detection systems that monitor for anomalous HTTP requests containing unusually long parameters or specific patterns indicative of buffer overflow attempts targeting CGI endpoints. By integrating these insights into threat modeling and vulnerability management programs, organizations can better anticipate how similar flaws might be exploited across other embedded devices with comparable architectural weaknesses.