CVE-2026-2908 is a stack-based buffer overflow vulnerability identified in the Tenda HG9 router, firmware version 300001138. The flaw exists in the Loopback Detection Configuration Endpoint, specifically in the /boaform/formLoopBack file, where improper validation or sanitization of the Ethtype parameter allows an attacker to overflow the stack buffer. This vulnerability can be triggered remotely over the network without requiring authentication or user interaction, making it highly exploitable. The overflow can corrupt memory, potentially enabling remote code execution or causing a denial of service by crashing the device. The vulnerability has been publicly disclosed, though no known exploits have been observed in the wild yet. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:L), no user interaction (UI:N), and high impact on confidentiality, integrity, and availability (VC:H/VI:H/VA:H). The absence of a patch or vendor advisory at this time means affected organizations must rely on compensating controls. The Tenda HG9 is a consumer and small business router, commonly deployed in residential and small office environments, which may be targeted for lateral movement or as a foothold in broader network attacks.

The impact of CVE-2026-2908 is significant due to its potential to allow remote attackers to execute arbitrary code or cause denial of service on affected Tenda HG9 routers. Successful exploitation compromises the confidentiality, integrity, and availability of the device, potentially allowing attackers to intercept or manipulate network traffic, disrupt network connectivity, or pivot into internal networks. This can lead to data breaches, network outages, and further compromise of connected systems. Since the vulnerability requires no user interaction and no authentication, it can be exploited by attackers scanning for vulnerable devices on the internet or internal networks. Organizations relying on Tenda HG9 routers, especially in critical network segments, face increased risk of targeted attacks or automated exploitation campaigns once exploits become widespread.

Given the lack of an official patch, organizations should implement the following mitigations: 1) Immediately isolate affected Tenda HG9 devices from untrusted networks, especially the internet, to reduce exposure. 2) Employ network-level filtering to block access to the /boaform/formLoopBack endpoint or restrict access to trusted management hosts only. 3) Monitor network traffic for unusual requests targeting the Ethtype parameter or signs of buffer overflow exploitation attempts. 4) Consider replacing Tenda HG9 devices with updated or alternative routers from vendors with active security support. 5) Apply network segmentation to limit the impact of compromised devices. 6) Keep firmware updated and monitor vendor advisories for patches or updates addressing this vulnerability. 7) Use intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability once available. These steps help reduce the attack surface and mitigate exploitation risk until a vendor patch is released.