CVE-2026-76869 in NR255-V
Summary
by MITRE • 09/16/2026
Netcore NR255-V version 1.5.130703 contains a stack-based buffer overflow in reboot_timer_set.cgi caused by improper sscanf token parsing. Attackers can exploit this flaw by submitting crafted input to the affected endpoint to corrupt stack memory.
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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 inadequate bounds checking within the device's firmware logic. Specifically, the issue resides in the reboot_timer_set.cgi script, which is responsible for handling configuration requests related to scheduled system reboots. This component processes user-supplied input by utilizing the sscanf function to parse tokens from incoming data streams. The fundamental technical error lies in the improper implementation of token parsing, where the application fails to validate the length or format of the input string before attempting to copy it into a fixed-size buffer located on the stack. This lack of rigorous validation allows an attacker to supply a crafted payload that exceeds the allocated memory space for the target variable.
From a technical perspective, this flaw is classified as a classic stack-based buffer overflow, which corresponds directly to Common Weakness Enumeration identifier CWE-121: Stack-based Buffer Overflow. When sscanf processes the oversized input without proper boundary checks, it writes data beyond the limits of the designated memory region on the call stack. This overwriting action corrupts adjacent memory locations, potentially overwriting critical control structures such as the return address or saved frame pointer. In embedded systems like routers and network devices, this corruption can lead to unpredictable behavior, including application crashes, denial of service conditions where the device becomes unresponsive, or more severely, arbitrary code execution if an attacker successfully manipulates the overwritten memory to redirect program flow to malicious shellcode injected via the same input vector.
The operational impact of exploiting this vulnerability is significant for network infrastructure integrity. Since reboot_timer_set.cgi is accessible through web interfaces often exposed to local networks and potentially the internet depending on configuration, it presents a viable attack surface. An attacker who gains access to this endpoint can trigger the overflow remotely without authentication if default credentials are in use or if other vulnerabilities exist that allow initial foothold establishment. Successful exploitation could result in the complete compromise of the device's operating system privileges. This allows the adversary to pivot into the internal network, intercept sensitive traffic, install persistent malware such as botnet clients, or disrupt critical connectivity services provided by the router. The stability of the entire local area network is jeopardized whenever this specific CGI script processes malformed data packets designed to trigger the memory corruption routine.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term secure development practices. The primary solution involves applying a firmware update released by Netcore that patches the sscanf implementation in reboot_timer_set.cgi with proper length validation functions such as snprintf or bounded string parsing routines that enforce strict character limits corresponding to the buffer size. In environments where patching is not immediately feasible, network-level controls should be implemented to restrict access to management interfaces from untrusted networks. Additionally, deploying intrusion detection systems configured to detect anomalous HTTP POST requests with unusually large payload sizes targeting CGI endpoints can provide a layer of defense against exploitation attempts. Future development cycles must incorporate static analysis tools and fuzzing techniques specifically targeted at embedded web server components to identify similar buffer handling weaknesses before deployment, aligning with secure coding standards such as OWASP guidelines for input validation and output encoding.