Netis NC63 firmware versions up to V3.0.0.3327 contain a stack-based buffer overflow in the login CGI handler. An attacker can submit an oversized Base64‑encoded password that exceeds the fixed-size stack buffer, causing the custom decoder to write past the end of the stack. The web server executes CGI scripts as root, so the overflow can be leveraged to inject code and obtain root privileges, leading to full system compromise.

The vulnerability affects Netis Systems’ NC63 router firmware up to version V3.0.0.3327. No other vendors or product lines are listed as impacted.

The CVSS score of 9.3 indicates high severity. The EPSS score is 1%, indicating a very low but non‑zero likelihood of exploitation; however, the exploit would still be trivial once the target is identified because the login endpoint is exposed via HTTP at /bin/netis.cgi and the attack requires no authentication. The vulnerability is not yet listed in the CISA KEV catalog, but the available evidence and high score suggest it should be treated as a high‑risk threat.