CVE-2026-35869 in Router AC450M
Summary
by MITRE • 08/27/2026
A Command Injection vulnerability exists in the bs_SetLimitCli_info function within the libshare.so library of LB-link Router AC450M V4.0.0. This flaw occurs due to insufficient validation and sanitization of user-supplied input before it is passed to a system-level command execution context. An attacker can exploit this vulnerability by injecting specially crafted shell metacharacters or payloads into the vulnerable parameter, resulting in the execution of arbitrary operating system commands.
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Analysis
by VulDB Data Team • 08/27/2026
The identified vulnerability represents a critical security flaw within the libshare.so library associated with LB-link Router AC450M V4.0.0, specifically located in the bs_SetLimitCli_info function. This component is responsible for handling client information and configuration limits, which are often exposed to network-facing interfaces or administrative consoles. The root cause of this vulnerability lies in a fundamental failure of input validation and sanitization protocols. When user-supplied data is received by this function, it is passed directly into a system-level command execution context without adequate filtering. This architectural oversight allows an attacker who can interact with the affected interface to inject malicious shell metacharacters or arbitrary payloads. Because the application does not distinguish between legitimate configuration parameters and executable code fragments, the underlying operating system interprets these injected strings as valid commands, leading to unauthorized remote code execution.
From a technical perspective, this flaw is classified under CWE-78, which denotes Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection. The vulnerability arises because the developer likely utilized unsafe functions such as system() or popen() with unsanitized input variables. In embedded router environments like those running LB-link firmware, these libraries often operate with elevated privileges to manage network settings and firewall rules. Consequently, successful exploitation grants an attacker a shell on the device with the same permissions as the vulnerable process. This typically means root-level access, allowing complete control over the target system. The lack of strict input validation is a common anti-pattern in firmware development where rapid deployment often supersedes rigorous security testing, leaving critical entry points exposed to manipulation via crafted HTTP requests or API calls that feed into this specific function.
The operational impact of exploiting this vulnerability is severe and comprehensive. An attacker can execute arbitrary commands on the router's operating system, which serves as the gateway for all connected devices in a local network. This capability enables several malicious outcomes beyond simple command execution. The attacker could modify DNS settings to redirect traffic through malicious servers, facilitating phishing or man-in-the-middle attacks against users relying on this connection. They may also install persistent backdoors, rootkits, or malware within the router's firmware storage, turning the device into a node for botnet activities such as Distributed Denial of Service (DDoS) attacks. Furthermore, since routers often manage firewall rules and access control lists, an attacker could disable security boundaries entirely, exposing internal network assets to external threats without detection. This transforms a single compromised endpoint into a strategic pivot point for broader network infiltration.
In terms of threat modeling, this vulnerability aligns with the MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques such as Unix Shell (T1059.004). The exploitation vector typically involves sending a specially crafted request to an exposed administrative interface or API endpoint that triggers the bs_SetLimitCli_info function. If this interface is accessible from the untrusted network side, which is common in poorly configured consumer routers, the attack surface expands significantly. Even if access requires authentication, weak default credentials are prevalent in such devices, making automated exploitation feasible for widespread botnets targeting IoT and networking hardware. The persistence of these vulnerabilities in legacy firmware versions highlights a critical gap in supply chain security and ongoing maintenance support from vendors like LB-link.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense is to apply the vendor-provided software update if available, as this vulnerability exists specifically in V4.0.0 of the firmware. If an official patch is not yet released, network administrators should restrict access to the administrative interface by disabling remote management features or limiting it to trusted IP addresses via firewall rules on upstream devices. Input validation must be implemented at the application layer before any data reaches system command execution functions; this includes whitelisting allowed characters and rejecting inputs containing shell metacharacters such as semicolons, pipes, ampersands, and backticks. For developers, adopting secure coding practices that avoid direct OS command invocation in favor of safer API calls or parameterized commands is essential to prevent recurrence. Regular security audits and static code analysis tools should be integrated into the firmware development lifecycle to detect such injection flaws early.