In 2019, I discovered multiple vulnerabilities in QNAP PhotoStation and CGI programs. These vulnerabilities can be chained into a pre-auth root RCE. All QNAP NAS models are vulnerable, and there are ~312K vulnerable QNAS NAS instances on the Internet (statistical prediction). These vulnerabilities have been responsibly reported, fixed and assigned CVE-2019–7192 (CVSS 9.8), CVE-2019–7193 (CVSS 9.8), CVE-2019–7194 (CVSS 9.8), CVE-2019–7195 (CVSS 9.8). This article is the first public disclosure, but only 3 of the vulnerabilities are disclosed, because they’re enough to achieve pre-auth root RCE.
The following Shodan search reveals 564K QNAP instances on the Internet. Among those, 590 of 1065 randomly chosen instances have Photo Station enabled. (checked via
GET /photo/slideshow.php and see if it responds with
Invalid album selection) Therefore, statistically speaking, with 95% confidence level, confidence interval 3, there should be ~312K instances having Photo Station enabled, and they were all vulnerable at the time (2019).
Affected Photo Station Versions
All downloadable versions before the fixed ones (6.0.3, 5.2.11, 5.4.9) were affected.
Visit QNAP’s Security Advisory for details like version info.
Now, let’s look at the 3 vulnerabilities that will later be chained to make a pre-auth root RCE.
Vulnerability 1: Pre-Auth Local File Disclosure (Effectively a Login Bypass)
This vulnerability enables an attacker to read arbitrary file on the server WITHOUT authentication.
The vulnerable code is in
exportFile simply outputs the file contents of
$source_file, whose suffix is fully controllable by the GET/POST parameter
filename. Therefore, we can read arbitrary file by specifying, say,
/share/./../etc/passwd, which is equivalent to
However, to reach the above vulnerable code, we need to pass the check
We need to avoid stepping into
exit(). So we need to:
- Get an album ID and access code of a publicly accessible album
- Load that album’s access code into
- Get the value of
Luckily, we can do all the above very easily WITHOUT any authentication!
Step 1 to Bypass CHECK_ACCESS_CODE: Album ID & Access Code
The following request creates a sample album and returns its album ID. This API is meant for sample albums, so it’s publicly accessible and it doesn’t require authentication:
The response contains the album ID, and it looks like:
Step 2, 3 to Bypass CHECK_ACCESS_CODE: Setting and Getting
The following sets
$_SESSION['access_code'] to the access code of the album we specify (
The populated access code (
POC: Pre-Auth Local File Disclosure
With the album ID and access code from the above, we can bypass
CHECK_ACCESS_CODE and read arbitrary files without authentication:
Upgrading the Pre-Auth Local File Disclosure to Privilege Escalation (Login Bypass)
We can use this pre-auth local file disclosure to read a magic file that contains a login token, which we can use to authenticate as a valid builtin user
token_ex = V2@rzKXK9vxyaQxpnRDbWYTyoYbi3DsIiby8mkbE1dCxDI=
- the file content won’t change after factory reset
- the file is generated when
/authLogin.cgi?app=xxx&sid=yyysucceeds for the first time
- PhotoStation caches a plaintext version of
$ cat /share/Multimedia/.@__thumb/ps.app.token
Therefore, we can use vulnerability 1 to read the cached plaintext token to bypass the login and authenticate as
With this trick, vulnerability 1 is actually an authentication bypass.
- Use the sample album feature to create and retrieve a public album ID, along with its access code (
- Use the album ID and access code to bypass
CHECK_ACCESS_CODEand trigger the LFD (Local File Disclosure) vulnerability to read arbitrary file
- Use the LFD to read
/share/Multimedia/.@__thumb/ps.app.tokenand use it to authenticate as
Vulnerability 2: Authenticated Session Tampering — Writing PHP Code to Session
Being authenticated as
appuser gives us access to the SMTP setting, which has an improper filtering in the email string. By setting an email to, for example,
<?=`$_POST[c]`?>@evil.com, an authenticated attacker can inject arbitrary PHP code into the session, this can be chained in the next vulnerability, or other file inclusion vulnerabilities (e.g.
POC: Authenticated Session Tampering
Vulnerability 3: (Pre-Auth) Writing Session to Arbitrary Location
This vulnerability enables an unauthenticated attacker to write session contents (serialized
$_SESSION) to arbitrary location on the server.
session_id() is fully controllable via cookie
QMS_SID. Therefore, the highlighted line would write an encoded (serialized) session into the file we specify.
POC: Writing Session to Arbitrary Location
The above works because
$musicStationSessionPath . ‘/sess_' . session_id() will become
/share/photostation/session/qts/sess_xxxxx/../../../../../mnt/ext/opt/photostation2/a.php, a publicly accessible file via the URL path
/photo/a.php. (thanks to
tsrm_realpath, because it will normalize
bbb, even if
sess_xxxxx doesn’t exist. This also caused phpMyAdmin 4.8.0~4.8.1 RCE that I found in 2018)
Chaining for Pre-Auth Root RCE
- Use vulnerability 1 to bypass authentication and authenticate as
- Use vulnerability 2 to put PHP code (via SMTP email) in PHP session (
- Use vulnerability 3 to write the polluted PHP session to Photo Station’s web directory to make a webshell
Now, you might ask: so where is that root permission? We’re only
I’m also surprised when I found this: the web server runs as root! Therefore, you can actually read
/etc/shadow using vulnerability 1.
A pity though: vulnerability 3 could’ve been a one-shot pre-auth root RCE. However, I couldn’t find a way to inject PHP code into
$_SESSION without authentication.
- 2019/06/14: reported technical details to QNAP
- 2019/12/16: vendor fixed all 4 vulnerabilities, offered to provide a bounty (the amount is concealed due to the bounty terms)
- 2019/12/31: got bounty
3 vulnerabilities are chained to get this pre-auth root RCE in QNAP PhotoStation, and it works on all QNAP’s NAS models. Several tricks for exploiting QNAP products are also disclosed. Hopefully QNAP fixes these tricks some day, otherwise I’m pretty sure there will be more high-CVSS CVEs coming up.
- UPGRADE YOUR QNAP NAS NOW, if you haven’t already
- Turn any file disclosure into authentication bypass by reading the magic file
- There is a way to decrypt
/etc/config/.app_token, but I’ll leave it as homework for you
- QNAP’s webserver runs as root
QMS_SIDmight give you some more 0days