ISO 27001:2022 Annex A 8.12: How to Stop Data Leaks Before They Happen
We have all been there. You are typing an email, you autocomplete the recipient’s name, hit send, and then feel that cold drop in your stomach. You just sent the confidential payroll spreadsheet to “John Smith” the external contractor, instead of “John Smith” the HR Director.
Accidents happen. But in the world of information security, accidents can be just as damaging as malicious attacks. This is exactly why ISO 27001:2022 Annex A 8.12 Data Leakage Prevention exists.
It is not just about stopping hackers from stealing your database; it is about stopping your own people (and systems) from accidentally sharing things they shouldn’t. Let’s break down what this control means and how you can implement it without bringing your business to a standstill.
Table of contents
What is Annex A 8.12?
In the 2022 update of the standard, Annex A 8.12 requires organisations to apply measures to detect and prevent the unauthorised disclosure or extraction of information. It is a preventive and detective control that focuses on protecting the confidentiality of your assets.
Think of it as the checkpoint at the airport. You have verified who the passengers are (Access Control), but you still need to scan their luggage to make sure they aren’t taking anything dangerous on the plane. DLP scans your outgoing data traffic to ensure no sensitive “luggage” (like credit card numbers, source code, or PII) is leaving the building unauthorized.
The Golden Rule: You Can’t Protect What You Don’t Know
Before you rush out and buy expensive DLP software, you need to take a step back. One of the biggest mistakes organisations make is trying to “prevent leaks” without defining what a “leak” actually looks like.
This control relies heavily on Data Classification (Annex A 5.12). If you haven’t labelled your documents as “Confidential,” “Internal,” or “Public,” your DLP tools won’t know what to block. You need to identify specific strings or patterns—such as National Insurance numbers, specific project keywords, or “Strictly Private” watermarks—so your systems can spot them.
For a complete list of how these controls interact, resources like ISO27001.com can provide a broader view of the framework.
How to Implement Data Leakage Prevention
Implementation isn’t a one-size-fits-all approach. It depends heavily on your risk appetite and your technology stack. However, a robust implementation usually covers these three areas:
1. Endpoint DLP
This lives on your laptops and servers. It monitors what users are doing directly on their machines.
- USB Drives: Can users copy 5GB of customer data to a thumb drive? If not, block USB write access.
- Copy/Paste: Should a remote support agent be able to copy a customer’s password and paste it into a personal notepad?
- Screenshots: Preventing screen capture of sensitive banking applications.
2. Network and Email DLP
This is the most common form of DLP. It involves scanning emails and web traffic.
- Email Scanning: If an attachment contains more than 10 credit card numbers, the email is automatically quarantined or encrypted.
- Web Uploads: Blocking users from uploading internal documents to personal cloud storage sites like Google Drive or Dropbox.
3. Cloud DLP
With everything moving to SaaS, you need to ensure that the files sitting in your Teams, SharePoint, or AWS buckets aren’t being shared publicly by mistake. Cloud DLP tools scan your repositories to check if a “Confidential” file has been created with a “Public Link” and automatically revoke that link if found.
Active Blocking vs. Monitoring
When you first turn on DLP controls, do not turn on active blocking immediately. If you do, you will almost certainly break a legitimate business process (like Finance trying to send a report to the bank).
Start in “Monitoring Mode.” Let the system run for a few weeks and generate logs. Review these logs to see what would have been blocked. Once you have tuned your rules to reduce false positives, then you can switch to “Blocking Mode.”
The Human Element
Annex A 8.12 isn’t just a technical control; it’s a cultural one. If your DLP system blocks an email, it should ideally tell the user why. A pop-up saying, “You are trying to send a document marked ‘Internal’ to an external email address” is a valuable training moment.
Sometimes, the “prevention” is simply asking the user for confirmation: “This looks like it contains sensitive data. Are you sure you want to send this?” This stops accidental leaks while allowing legitimate business to continue.
Conclusion
Data Leakage Prevention is one of the most powerful tools in the ISO 27001 arsenal. It provides the assurance that even if a user account is compromised or an employee makes a careless mistake, there is a safety net in place to catch your most valuable data before it walks out the door. Start small, classify your data, and tune your tools carefully.
