Remote Code Execution in Apache UNO API
During his research on the potential use of DCOM for lateral movement in Windows networks, our very talented intern Axel Boesenach discovered that the Apache UNO API (used by both OpenOffice and LibreOffice in so-called ‘office server’ mode) allows anyone to send it system commands, without any form of authentication, and it will execute the command with the rights of the user running OpenOffice or LibreOffice in ‘office server’ mode.
CVE reference: | not yet assigned (see below) |
CVSS score: | 9.8 (critical) |
CVSS vector: | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
Affected systems
- Apache OpenOffice, all recent versions including current version 4.1.6, all platforms
- LibreOffice, all recent versions including current version 6.2.0 / 6.1.5, all platforms
We don’t know when the vulnerable API was introduced. Code for it seems to be 5 years old, judging from timestamps.
Note that normal use of OpenOffice or LibreOffice as a “client” does not expose this vulnerability. OpenOffice/LibreOffice must explicitly be told to run as an “office server” and to listen on a network port for it to expose this API call.
Overview
The Apache UNO API is exposed to the network if OpenOffice or LibreOffice is run as an “office server” using a command such as this:
The API contains a call named XSystemShellExecute which will execute an arbitrary command sent to it as a parameter. No authentication is required, only knowledge of the protocol.
Details (without Proof-of-Concept code for now) is available in Axel’s blog post.
Impact
The impact of this issue can be severe. Any user account used to launch OpenOffice or LibreOffice in office server mode can be compromised with relative ease.
There are two mitigating factors:
- The “office server” mode is rarely used
- Although examples tend to use port numbers just above 2000, there is no default port number, so scanning for this issue is not trivial.
Solution
Unfortunately, after five months of trying, we have not been able to convince the Apache Security Team that this is, in fact, a security issue. So there is no patch.
This is also why there is no CVE number. Apache assigns their own CVE numbers (they are a “CNA”, a “CVE Numbering Authority”, themselves), and they are not recognising this as a security issue.
We can only recommend, if using OpenOffice or LibreOffice in server mode is absolutely necessary, to use a firewall (possibly host-based) to limit which systems can connect to the API, and to run it in a container using a low-priviliged user account.
We have also made available a Snort rule to detect the use of this API call on your network:
Technical details
See Axel’s excellent blog post for many more details of this issue.
Responsible disclosure timeline
- 18-Sep-2018: RCE disclosed to Apache Security Team
- 06-Dec-2018: E‑mailed Apache to ask about the status of investigation
- 11-Dec-2018: Apache said they are aiming for a new release in January, asking us to postpone the disclosure of the RCE until 31-Jan-2019
- 18-Dec-2018: New OpenOffice release (4.1.6) without a fix for this issue or any communications from Apache
- 25-Jan-2019: E‑mailed Apache to ask about the status of investigation
- 05-Feb-2019: Received e‑mail from Apache that they don’t consider this to be a security issue because the configuration is so uncommon, but are willing to work together to fix this in OpenOffice 4.1.7
- 07-Feb-2019: E‑mailed Apache to confirm that we’re willing to work with them on this issue
- 22-Feb-2019: E‑mailed Apache to let them know we’re planning to release
- 27-Feb-2019: Release of this post and advisory
Vendor advisory
None as yet.