Slack security review

Created:  11 Jun 2018
Updated:  11 Jun 2018
Slack logo
A security review of the Slack real-time messaging and file sharing application, based on the NCSC's SaaS security principles.

Slack is a real-time messaging and file sharing application designed to aid group collaboration. 


How Slack performs against the SaaS Principles




Does the SaaS provider protect external data in transit using TLS?


According to their white paper Slack uses TLS 1.2 to protect external data.

Does the SaaS provider protect external data in transit using correctly configured certificates?


Slack meets the recommended cryptographic profiles for TLS as published by the NCSC. In addition the Slack domain currently gets an 'A+' rating from Qualys SSL Labs. Note that this was performed on their top level domain, and not all subdomains that may be used for API calls.

Does the SaaS provider protect internal data in transit between services using encryption?


Slack's white paper only discusses data in transit on public networks or at rest.

Does the SaaS provider protect internal data in transit between services using correctly configured certificates? 


It is not known if Slack protects data in transit.

If APIs are available, does the SaaS provider protect both internal and external APIs through an authentication method?


All API requests made to Slack need a valid OAuth token as described in the API documentation.

If there is a concept of privilege levels in the service, does the SaaS provider have the ability for low privilege users to be created?


Users can have one of several roles with varying levels of permissions. This is described in the Slack documentation.
If there is a concept of privilege levels, does the SaaS provider provide 2FA/multi-factor authentication on at least the high privileged accounts?


Slack currently provides multi-factor authentication via SMS or any app that supports TOTP (Such as Google Authenticator). Slack also supports SSO (Single Sign On), therefore multi factor authentication may be possible by that method if the SSO provider supports it. For the non-free tier, multi-factor authentication is mandatory for all users if enabled by an administrator.

Does the SaaS provider collect logs of events?

Types of log may include security logs and resource logs


Slack's white paper states that logging is performed on all production and corporate infrastructure and then stored in a separate network for analysis by their security team. 
Does the provider make logs available to the client?


Slack provides an API that details how to retrieve access logs for your instance.

Does the SaaS provider have a clear incident response and patching system in place to remedy any publicly reported issues in their service, or libraries that the service makes use of?

The provider’s previous track record on this is a good metric to see how they’ll cope with a new issue occurring.



Slack has a dedicated CSIRT (Computer Security Incident Response Team) according to their white paper. They also have a public bug bounty program via HackerOne.
Does the SaaS provider give clear and transparent details on their product and the implemented security features (i.e. how easy has it been to answer the above questions) ? Yes Slack publishes details of their security architecture in their white paper.


Exporting data

Slack's documentation on exporting data from the service can be found on the Slack Help Center.

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