CVE-2026-51603: Stack-based Buffer Overflow

A stack-based buffer overflow vulnerability in the RTSP service of Tenda CP3 V3.0 (firmware V31.1.9.91) allows an unauthenticated remote attacker to cause a denial of service via a crafted second SETUP request. After completing the OPTIONS, DESCRIBE, and a legitimate first SETUP request to obtain a valid session ID, the RTSP service's second-stage URL routing parser fails to validate the length of the URL field in the subsequent SETUP request. By supplying a URL consisting of exactly four consecutive repetitions of a valid RTSP URL, an attacker can bypass first-stage format validation and trigger a stack buffer overflow, causing an immediate crash of the RTSP service process and rendering the device inaccessible to all clients on the local network.