This Thunderbird extension warnst against potential malicious attachments like docm and xlsm files. A set of highly risky attachments are blocked (cmd, exe etc.). See corresponding section in this document for an overview of file extensions.
There is a lot of space for improvements. Feel free to contribute and send pull requests.
Special thanks to Sarah ( www.astriia.de ) for creating the logo!
This extension can be downloaded directly from the Thunderbird add-on repository: https://addons.thunderbird.net/de/thunderbird/addon/warnattachment/
Warning Message Extensions
A warning message is shown for the following file extensions:
These files may contain macro viruses which are nowadays commonly used for encryption malware. The user is asked if s/he is really willing to open the file and if it is from a trustworthy source.
Block Message Extensions
The following extensions are blocked completely. The user is not able to open these files (besides deactivating the plugin). The source of these file types is this google mail support page:
The user can not open attachments with these extensions.
To test the extension without installing the xpi file, you can either copy the
complete directory into you
extensions directory, i.e., the
email@example.com. Alternatively, you can create a text file named
firstname.lastname@example.org into your extension directory. In that file, you
should provide the absolute path to the git repository like for example
Further information can be found on the mozilla developer webpage
chrome.manifest contains the references to the localization files as well
as to the content of the application. These references differ depending on the
For building the
*.xpifile, the references need to point to the compressed archives. This is the default setting in the
chrome.manifest. These settings are also stored in the file
chrome.manifest.compressedwhich can be used to recover the original settings.
For developing (without creating the
*.xpifile for each step), the extension can be used in an uncompressed way (see previous step). For this, the references in the
chrom.manifestneed to be adapted as done in the file
chrome.manifest.uncompressed. Copy this file over the original
chrome.manifestand add the link as mentioned before to the profile / extension directory. Do not forget to change back to the
chrome.manifest.compressedbefore creating the
To build the
.xpi extension file, simply run
make in the root directory of
For convenience, the binaries are provided in the bin directory.
WarnAttachment is tested using several versions of Thunderbird on a Linux (Debian-based) system. Currently (October 2018), the following Thunderbird versions are tested (subject to change):
- Thunderbird 38 (German)
- Thunderbird 52 (German)
- Thunderbird 60 (German, US-English)
For changes, check the CHANGELOG.md file in the current directory
- The configuration dialog should be extended
- Prevent saving files and not just opening
Jens Dede email@example.com, 2018
This code is licensed under the GPLv3