safelinks

Go-based tooling to manipulate (e.g., normalize/decode) Microsoft Office 365 "Safe Links" URLs.

Table of Contents

• Project home
• Overview
• Features
  • usl CLI tool
  • dsl CLI tool
  • dslg GUI tool
  • eslg GUI tool
• Changelog
• Requirements
  • Building source code
  • Running
• Installation
  • From source
  • Using release binaries
  • Deployment
• Configuration
  • Command-line arguments
    • usl
      • Flags
      • Positional Argument
      • Standard input (e.g., "piping")
      • Without arguments or flags
    • dsl
      • Flags
      • Positional Argument
      • Standard input (e.g., "piping")
      • Without arguments or flags
    • dslg
    • eslg
• Examples
  • usl tool
    • Using url positional argument
    • Using url flag
    • Using input prompt
    • Using standard input (e.g., "piping")
    • Using filename flag
    • Verbose output
  • dsl tool
    • Using url positional argument
    • Using url flag
    • Using input prompt
    • Using standard input (e.g., "piping")
    • Using filename flag
  • dslg tool
  • eslg tool
• License
• References
  • General
  • Observed safelinks.protection.outlook.com subdomains
  • Alternative decoders

Project home

See our GitHub repo for the latest code, to file an issue or submit improvements for review and potential inclusion into the project.

Overview

This repo is intended to provide various tools used to manipulate (e.g., normalize/decode) Microsoft Office 365 "Safe Links" URLs.

Tool Name	Overall Status	Description
usl	🆗Beta	Small CLI tool for decoding a given Safe Links URL.
dsl	💥Alpha	Small CLI tool for decoding Safe Links URLs within input text.
dslg	💥Alpha	GUI tool for decoding Safe Links URLs within input text.
eslg	💥Alpha	GUI tool for encoding normal URLs within input text for testing purposes.

Features

usl CLI tool

Small CLI tool for decoding a given Safe Links URL.

• Specify single Safe Links URL
  • via positional argument
  • via flag
  • via interactive prompt
• Specify multiple bare Safe Links URLs (no surrounding text)
  • via interactive prompt
  • via standard input ("piping")
  • via file (using flag)
• Optional verbose listing of query parameter values within a given Safe Links URL.

dsl CLI tool

Small CLI tool for decoding Safe Links URLs within surrounding input text.

• Specify single Safe Links URL
  • via positional argument
  • via flag
  • via interactive prompt
• Specify multiple Safe Links URLs (with surrounding text untouched)
  • via interactive prompt
  • via standard input ("piping")
  • via file (using flag)

dslg GUI tool

GUI tool for decoding Safe Links URLs within given input text.

• Specify single Safe Links URL
• Specify multiple Safe Links URLs (with surrounding text untouched)

eslg GUI tool

GUI tool for generating test data.

Changelog

See the CHANGELOG.md file for the changes associated with each release of this application. Changes that have been merged to master, but not yet an official release may also be noted in the file under the Unreleased section. A helpful link to the Git commit history since the last official release is also provided for further review.

Requirements

The following is a loose guideline. Other combinations of Go and operating systems for building and running tools from this repo may work, but have not been tested.

Building source code

• Go
  • see this project's go.mod file for preferred version
  • this project tests against officially supported Go releases
    • the most recent stable release (aka, "stable")
    • the prior, but still supported release (aka, "oldstable")
• GCC
  • if building with custom options (as the provided Makefile does)
• mingw-w64
  • if building GUI app(s) for Windows
  • used to perform CGO-enabled builds of Fyne (GUI) applications
• make
  • if using the provided Makefile
• Fyle toolkit OS dependencies
  • see https://docs.fyne.io/started/ for OS-specific packages

Tip

Use make docker-release-build or podman-release-build Makefile recipes to generate/use build containers compatible with this project.

Running

The CLI apps are broadly compatible but have been tested against:

• Microsoft Windows 10
• Ubuntu 20.04

The GUI app(s) have been tested against:

• Microsoft Windows 10
• Microsoft Windows 11
• Ubuntu 20.04
  • libgl1 package was needed

Note

The build image used by this project has an inherited dependency on the official upstream Go Docker image and shares that image's minimum glibc version requirement.

As of this writing, a glibc release of version 2.31 or newer is required to match the Debian 11 base image used by current Go Docker images. Ubuntu 20.04 has glibc 2.31 and meets this requirement. Older distro versions may not meet this requirement and will require building from source.

Important

When the upstream Go Docker image swaps out the minimum Debian base image OS (currently Debian 11) this may also mean dropping support for some Linux distros.

Installation

From source

Tip

Use docker-release-build or podman-release-build Makefile recipes to use build containers compatible with this project.

1. Download Go
2. Install Go
3. Clone the repo
   1. cd /tmp
   2. git clone https://github.com/atc0005/safelinks
   3. cd safelinks
4. Install dependencies (optional)
   • for Ubuntu Linux
     • if building for the current architecture
       • sudo apt-get install make gcc xz-utils libgl1-mesa-dev xorg-dev
     • if building x86 binaries on x64 OS
       • sudo dpkg --add-architecture i386
       • sudo dpkg --configure -a
       • sudo apt-get update
       • sudo apt-get install make bsdmainutils gcc gcc-multilib gcc-mingw-w64 xz-utils libgl1-mesa-dev xorg-dev
       • sudo apt-get install libxinerama-dev:i386 libgl1-mesa-dev:i386 libxrandr-dev:i386 libxxf86vm-dev:i386 libxi-dev:i386 libxcursor-dev:i386
   • for CentOS Linux
     1. sudo yum install make gcc libXcursor-devel libXrandr-devel mesa-libGL-devel libXi-devel libXinerama-devel libXxf86vm-devel
5. Build
   • for the detected current operating system and architecture, explicitly using bundled dependencies in top-level vendor folder
     • most likely this is what you want (if building manually)
     • go build -mod=vendor ./cmd/usl/
     • go build -mod=vendor ./cmd/dsl/
     • go build -mod=vendor ./cmd/dslg/
     • go build -mod=vendor ./cmd/eslg/
   • manually, explicitly specifying target OS and architecture
     • GOOS=linux GOARCH=amd64 go build -mod=vendor ./cmd/usl/
       • substitute GOARCH=amd64 with the appropriate architecture if using different hardware (e.g., GOARCH=arm64 or GOARCH=386)
       • substitute GOOS=linux with the appropriate OS if using a different platform (e.g., GOOS=windows)
     • GOOS=linux GOARCH=amd64 go build -mod=vendor ./cmd/dsl/
     • GOOS=linux GOARCH=amd64 go build -mod=vendor ./cmd/dslg/
     • GOOS=linux GOARCH=amd64 go build -mod=vendor ./cmd/eslg/
   • using Makefile all recipe
     • make all
       • generates x86 and x64 binaries
   • using Makefile release-build recipe
     • make release-build
       • generates the same release assets as provided by this project's releases
6. Locate generated binaries
   • if using Makefile
     • look in /tmp/safelinks/release_assets/usl/
     • look in /tmp/safelinks/release_assets/dsl/
     • look in /tmp/safelinks/release_assets/dslg/
     • look in /tmp/safelinks/release_assets/eslg/
   • if using go build
     • look in /tmp/safelinks/
7. Copy the applicable binaries to whatever systems needs to run them so that they can be deployed

Note

Depending on which Makefile recipe you use the generated binary may be compressed and have an xz extension. If so, you should decompress the binary first before deploying it (e.g., xz -d usl-linux-amd64.xz).

Using release binaries

1. Download the latest release binaries
2. Decompress binaries
   • e.g., xz -d usl-linux-amd64.xz
   • 7-Zip also works well for this on Windows systems (e.g., for systems without Git for Windows or WSL)
3. Copy the applicable binaries to whatever systems needs to run them so that they can be deployed

NOTE:

DEB and RPM packages are provided as an alternative to manually deploying binaries.

Deployment

1. Place usl in a location where it can be easily accessed
2. Place dsl in a location where it can be easily accessed
3. Place dslg in a location where it can be easily accessed
4. Place eslg in a location where it can be easily accessed

Note

The libgl1 package is needed on target Ubuntu systems for the dslg and eslg apps.

Configuration

Command-line arguments

• Use the -h or --help flag to display current usage information.
• Flags marked as required must be set via CLI flag.
• Flags not marked as required are for settings where a useful default is already defined, but may be overridden if desired.

Note

🛠️ The dsl tool does not support CLI arguments but may do so in the future.

usl

Flags

Flag	Required	Default	Repeat	Possible	Description
h, help	No	false	No	h, help	Show Help text along with the list of supported flags.
version	No	false	No	version	Whether to display application version and then immediately exit application.
v, verbose	No	false	No	v, verbose	Display additional information about a given Safe Links URL.
u, url	maybe		No	u, url	Safe Links URL to decode
f, inputfile	maybe		No	valid path to file	Path to file containing Safe Links URLs to decode

NOTE: If an input url is not specified (e.g., via flag, positional argument or standard input) a prompt is provided to enter a Safe Links URL.

Positional Argument

A URL pattern is accepted as a single positional argument in place of the u or url flag. It is recommended that you quote the URL pattern to help prevent some of the characters from being interpreted as shell commands (e.g., & as an attempt to background a command).

Standard input (e.g., "piping")

One or more URL patterns can be provided by piping them to the usl tool.

An attempt is made to decode all input URLs (no early exit). Successful decoding results are emitted to stdout with decoding failures emitted to stderr. This allows for splitting success results and error output across different files (e.g., for later review).

Without arguments or flags

The usl tool can also be called without any input (e.g., flags, positional argument, standard input). In this scenario it will prompt you to insert/paste the URL pattern (quoted or otherwise).

dsl

Important

This tool is in early development and behavior is subject to change.

Flags

Note

🛠️ This feature is not implemented but may be added in the future.

Positional Argument

Note

🛠️ This feature is not implemented but may be added in the future.

Standard input (e.g., "piping")

Text with interspersed URLs (separated by whitespace) can be provided for decoding by piping it to the dsl tool. Output is sent to stdout.

Each matched Safe Links URL is replaced with a decoded version leaving surrounding text as-is.

Without arguments or flags

The dsl tool can also be called without any input. In this scenario it will prompt you to insert/paste content for decoding.

If no input is provided for a the listed amount of time the dsl tool will timeout and exit.

dslg

No command-line arguments are currently supported.

eslg

No command-line arguments are currently supported.

Examples

usl tool

Though probably not required for all terminals, we quote the Safe Links URL to prevent unintended interpretation of characters in the URL.

Using url positional argument

$ usl 'SafeLinksURLHere'
https://go.dev/dl/

Using url flag

$ usl --url 'SafeLinksURLHere'
https://go.dev/dl/

Using input prompt

In this example we just press enter so that we will be prompted for the input URL pattern.

$ usl
Enter URL: SafeLinksURLHere
https://go.dev/dl/

Using standard input (e.g., "piping")

$ cat file.with.links | usl
https://go.dev/dl/
http://example.com
http://example.net

$ echo 'SafeLinksURLHere' | usl
https://go.dev/dl/

Using filename flag

$ usl --filename file.with.links
https://go.dev/dl/
http://example.com
http://example.net

Verbose output

$ usl --verbose --url 'SafeLinksURLHere'

Expanded values from the given link:

  data      : PLACEHOLDER
  host      : nam99.safelinks.protection.outlook.com
  reserved  : 0
  sdata     : PLACEHOLDER
  url       : https://go.dev/dl/

dsl tool

Using url positional argument

Note

🛠️ This feature is not implemented but may be added in the future.

Using url flag

Note

🛠️ This feature is not implemented but may be added in the future.

Using input prompt

In this example we just press enter so that we will be prompted for the input URL pattern.

$ dsl
Enter single or multi-line input. Press Ctrl-C to stop (or wait 15s for timeout).

  - Feedback from this app is sent to stderr.
  - Decoding results are sent to stdout.
  - Tip: Redirect stdout to a file for multiple input lines.

Not shown is the copy/pasted content with Safe Links encoded URLs interspersed (e.g., right-click pasted into console).

Using standard input (e.g., "piping")

$ cat file.with.mixed.text.content | dsl
tacos are great https://go.dev/dl/ but so are cookies http://example.com

$ echo 'SafeLinksURLHere' | dsl
https://go.dev/dl/

$ dsl < file.with.mixed.text.content > decoded-output.txt
tacos are great https://go.dev/dl/ but so are cookies http://example.com

Using filename flag

Note

🛠️ This feature is not implemented but may be added in the future.

dslg tool

1. Launch application
2. Copy single URL or mix of URLs and text (e.g., copying an email) into the input field
3. Press Decode button
4. Press Copy to Clipboard button
5. Paste decoded text where needed (e.g., a ticket)

Warning

The Copy to Clipboard action does not preserve any existing clipboard content; there is no undo for using this button

eslg tool

1. Launch application
2. Copy single unencoded URL or mix of unencoded URLs and text (e.g., copying an email) into the input field
3. Press one of the desired "action" buttons
   • Encode All
   • Encode Randomly
   • QueryEscape All
   • QueryEscape Randomly
4. Press Copy to Clipboard button
5. Paste transformed text where needed (e.g., a new testdata file)

Warning

The Copy to Clipboard action does not preserve any existing clipboard content; there is no undo for using this button

License

See the LICENSE file for details.

References

General

• https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/safe-links-about
• https://learn.microsoft.com/en-us/training/modules/manage-safe-links/
  • https://learn.microsoft.com/en-us/training/modules/manage-safe-links/6-examine-end-user-experience-with
• https://security.stackexchange.com/questions/230309/is-a-safelinks-protection-outlook-com-link-phishing
  • https://security.stackexchange.com/a/230371
• https://techcommunity.microsoft.com/t5/security-compliance-and-identity/data-sdata-and-reserved-parameters-in-office-atp-safelinks/td-p/1637050

Observed safelinks.protection.outlook.com subdomains

The following *.safelinks.protection.outlook.com subdomains have been found listed on various KB articles and forums:

• emea01
  • https://answers.microsoft.com/en-us/outlook_com/forum/all/how-do-i-stop-emea01safelinksprotectionoutlook/32832d4f-e57f-4d3e-9e9e-cc967abdc15e
• eur04
  • https://techcommunity.microsoft.com/t5/security-compliance-and-identity/data-sdata-and-reserved-parameters-in-office-atp-safelinks/m-p/1637050
• na01
  • https://kb.uconn.edu/space/IKB/10730111028/Office+365+Safe+Links%3A+Advanced+Threat+Protection
• nam01
  • https://meta.discourse.org/t/stripping-outlook-safe-link-urls/258114
  • https://answers.microsoft.com/en-us/msoffice/forum/all/safelink-url-decode-api/9e7d7ef9-261f-41c3-a352-198309f02641
• nam02
  • https://answers.microsoft.com/en-us/outlook_com/forum/all/safelinks-one-answer/8eb833c1-53dc-4c98-9c89-ff2f9c8dc812
  • https://security.stackexchange.com/questions/230309/is-a-safelinks-protection-outlook-com-link-phishing
• nam04
  • https://answers.microsoft.com/en-us/outlook_com/forum/all/safelinks-redirect-to-https-rather-than-http/9bcd5342-11cc-4eca-9675-336f0c45c488
• nam10
  • https://kb.uconn.edu/space/IKB/10803643182/Test+a+Link+%2F+Decoding+SafeLinks+URLs
• nam11
  • https://it.arizona.edu/news/new-security-feature-urls-outlook-email
• nam12
  • https://it.cornell.edu/news/microsoft-safe-links-will-soon-provide-more-protection-against-malicious-links/20230913

Alternative decoders

The following alternative tools were encountered while researching valid Safe Links subdomains. These tools are listed here for informational purposes; no endorsement is implied.

Important

No guarantees are made regarding the functionality or privacy policies of the following online or local tools. YMMV.

Online decoders:

• https://safelinks.apps.buffalo.edu/
• https://digital.va.gov/employee-resource-center/safe-link-decoder/
• https://wmich.edu/oit/converter/
• https://it.cornell.edu/decode
• https://www.ohio.edu/oit/security/safe-computing/identifying-malicious-email/safelinks-decoder
• https://www.umsystem.edu/forms/safe-link-decoder
• https://stockton.edu/omni-cms-support/safelinks-decoder.html
• https://infosecurity.utdallas.edu/safelink/

Local decoders:

• https://github.com/franta/atp-safelinks
• https://github.com/infosecB/normalize-atp-safelink
• https://gist.github.com/milnak/5100fd003fa3f9281e8f417a1cd46fde