# H3C Magic R300-2100M was discovered stack overflow via the UpdateSnat interface at /goform/aspForm
###### tags: `H3C` `Magic R300-2100M`
author:Yifeng Li，Wolin Zhuang;
## Vulnerability Description
H3C Magic R300-2100M firmware version R300-2100MV100R004 was discovered to contain a stack overflow via the UpdateSnat interface at /goform/aspForm.
## Vulnerability Details
In the UpdateSnat function, local variable v11 is 64 bytes long.
V9 can be controlled by attacker, entered as parameter 'param'.
In line 20, v9 is formatted into v11 by function sscanf as long as
the size of the data we enter is less than 512 bytes. So when the size of the data we enter is larger than 64 bytes and less than 512 bytes, it will cause a stack overflow.
## Recurring vulnerabilities and POC
In order to reproduce the vulnerability, the following steps can be followed:
1. Upgrade router Magic_R300-2100M to newest firmware(we have a physical machine)
2. Login to 192.168.124.1 as admin
3. Attack with the following POC
POST /goform/aspForm HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.5304.107 Safari/537.36
Accept-Encoding: gzip, deflate
Cookie: USERLOGINIDFLAG=; LOGIN_PSD_REM_FLAG=; UPGRADE_SOURCE=
By sending delicately constructed data package as the poc above, we can cause a stack overflow error, leading to the crash of webs progress.
And you can write your own exp to get the root shell.