| Title | Tenda HG9 V300001138 Stack-based Buffer Overflow |
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| Description | During a security review of the Tenda HG9 router firmware (version V300001138), a critical stack-based buffer overflow vulnerability was identified in the Loopback Detection configuration endpoint /boaform/formLoopBack.
The vulnerability exists in the handling of the Ethtype parameter. When the apply parameter is present, the function eventually checks for the Ethtype parameter. It retrieves the user-supplied string and uses sprintf to format it as a hexadecimal string (prepending "0x") into a local stack buffer named v20.
The destination buffer v20 is declared with a tiny fixed size of 8 bytes. The code intends to parse a 2-byte hexadecimal Ethernet type (e.g., "0800"), which would result in a 6-byte string ("0x0800"). However, there is no validation of the input length. If an attacker provides an Ethtype string longer than 5 bytes, the sprintf function will write past the end of v20, overflowing the stack buffer and overwriting adjacent stack variables, including the saved return address. |
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| Source | ⚠️ https://github.com/QIU-DIE/cve-nneeww/issues/10 |
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| User | LINXI666 (UID 91556) |
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| Submission | 02/10/2026 08:30 (3 months ago) |
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| Moderation | 02/20/2026 21:15 (11 days later) |
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| Status | Accepted |
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| VulDB entry | 347217 [Tenda HG9 300001138 Loopback Detection Configuration Endpoint /boaform/formLoopBack Ethtype stack-based overflow] |
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| Points | 20 |
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