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Date: Mon, 24 Oct 2022 14:53:05 +0200
From: Matthias Gerstner <>
Subject: Warpinator remote file creation / overwrite security issue

Hello list,

this report is about a remote file creation / overwrite issue I found in
Warpinator [1]. The release under review for this report was Warpinator
version 1.2.13.

1) About Warpinator

Warpinator is a graphical application to easily transfer files between
hosts on a local network in a decentralized manner. To find other users
on the network a zeroconf protocol is used.

2) Connection Setup and Trust Model

The main connection between two instances of Warpinator is established
using SSL. To establish trust a shared symmetric key derived from what
is called a "group code" is used. Each instance of Warpinator provides a
randomly generated public SSL certificate in an encrypted form over the
network. It is encrypted symmetrically based on the group code via the
libsodium "SecretBox" API. According to libsodium documentation [2] this
API employs the following cryptographic algorithms:

Encryption: XSalsa20 stream cipher
Authentication: Poly1305 MAC

Although it seems unusual to make the public SSL certificate actually
secret in this approach it seems safe in so far as without it no one
will be able to establish the encrypted SSL connection. Once the SSL
connection is established no further authentication or authenticity
checks happen in the Warpinator RPC protocol.

An issue with the group code, though, is that is has the default value
of "Warpinator". The project's README of the reviewed version states:

    Do not leave it as the default "Warpinator".

During runtime the application does not undertake any efforts to bring
this to the user's attention, but starts to operate using the default
group code right away. A user has to consciously change this group code
in the settings dialog to achieve a trusted setup. Therefore I fear
there is a high risk of users keeping this default setup and thus
possibly trusting arbitrary other instances of Warpinator on the same

This could allow malicious actors on the same network to act as a
man-in-the-middle to intercept transferred data. The authenticity of the
randomly generated SSL certificates used is not verified otherwise by
Warpinator as far as I can see, so the group code is the only means of
establishing trust between Warpinator instances.

3) File Creation / Overwrite Issue (CVE-2022-42725)

I noticed that Warpinator does not manage to confine uploaded data
properly to the configured upload directory (~/Warpinator by default).
Warpinator trusts the remote Warpinator instance regarding the path
names and other metadata that are transferred. Furthermore the
file information displayed in confirmation dialogs is not necessarily
reflecting what the peer is actually sending.

The following code change allows a simple demonstration of this:

  diff --git a/src/ b/src/
  index 0996738..dc27433 100644
  --- a/src/
  +++ b/src/
  @@ -138,7 +138,7 @@ class FileSender(GObject.Object):
                               time = None

  -                        yield warp_pb2.FileChunk(relative_path=file.relative_path,
  +                        yield warp_pb2.FileChunk(relative_path="../.bashrc",

This patch simply unconditionally changes the `relative_path` field
reported during uploads to "../.bashrc". If a file is sent from a
malicious Warpinator instance using this changed code then the uploaded
file content will appear on the victim's system in $HOME/.bashrc,
without the user being aware of this from GUI messages. It will solely
be confusing, because the uploaded file will not appear under the
expected name. This way a malicious remote Warpinator instance can
achieve full remote code execution in the context of the user account
running Warpinator on the victim's system.

There is a configuration setting in Warpinator "Require approval when
files would be overwritten", which is active by default. The check for
file overwrite actually happens before the actual file and relative_path
are transferred, thus this setting does not prevent the described

Should a user decide to disable another setting "Require approval before
accepting files" then the described attack would even work fully
unattended, without any interactive confirmation by the victim user. The
only precondition is that the attacker knows the correct group code to
interact with the victim.

To get by the confirmation dialog a likely scenario would be social
engineering attacks where the attacker suggests to send over a file
using Warpinator but actually overwrites arbitrary data of the victim's
user account.

4) Bugfix

Upstream implemented some first aid changes for the file overwrite issue
in [3], [4], [5], [6]. This should prevent the naive attack outlined in
this report. There are remaining concerns, however:

- Warpinator implements a complex file transfer protocol that even
  allows to create complete directory trees including symlinks on the
  remote node. Also Warpinator employs thread pools for processing
  incoming requests potentially in parallel, thus it could be possible
  to circumvent the added security checks by exploiting race conditions
  (e.g. creating a symlink in one file transfer that is followed in
  another). I did not further explore these possibilities.
- To my knowledge the issue with the default group code described in 2)
  is still not addressed. Changing the group code is vital to reduce the
  potential attack surface. The interactive workflow of Warpinator
  should foster this, or not set a default group code at all.

I want to thank Warpinator upstream for looking into the issue and
dealing with my report. Upstream is still investigating and discussing
how to best address the remaining concerns. The initial fixes and CVE
assignment are already public for a while now so we decided to publish
the full report. As far as I am aware there is no release available yet
containing these initial fixes.

5) Timeline

2022-09-01: a routine review [7] was requested for addition of Warpinator
            to openSUSE Tumbleweed.
2022-09-15: I discovered the file overwrite issue described in this
            report and started getting into contact with upstream.
2022-09-16: I sent the full report to the Warpinator main developer and
            Linux Mint security contact. I offered coordinated
2022-09-22: I reviewed the initial patches by upstream and upstream
            published them on GitHub. No formal coordinated disclosure
	    process has been setup.
2022-10-06: A colleague from the SUSE security team requested a CVE from
            Mitre to track this issue.
2022-10-19: No final solution has been found yet in discussions with
            upstream to address the remaining concerns. We gave some
	    ideas as input but also asked to publish the full
	    vulnerability report soon to make the community fully aware.


Best Regards


Matthias Gerstner <>
Security Engineer
GPG Key ID: 0x14C405C971923553
SUSE Software Solutions Germany GmbH
HRB 36809, AG Nürnberg
Geschäftsführer: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman

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