Known limitations in Conditional Access app control
This article describes known limitations for working with Conditional Access app control in Microsoft Defender for Cloud Apps.
To learn more about security limitations, contact our support team.
Maximum file size for session policies
You can apply session policies on files that have a maximum size of 50 MB. For example, this maximum file size is relevant when you're defining policies to monitor file downloads from OneDrive, block file updates, or block downloads or uploads of malware files.
In cases like these, be sure to cover files that are larger than 50 MB by using the tenant settings to determine whether the file is allowed or blocked, regardless of any matching policies.
In Microsoft Defender XDR, select Settings > Conditional Access App Control > Default behavior to manage settings for files that are larger than 50 MB.
Maximum file size for session policies based on content inspection
When you apply a session policy to block file uploads or downloads based on content inspection, the inspection is performed only on files that are smaller than 30 MB and that have fewer than 1 million characters.
For example, you might define one of the following session policies:
- Block upload of files that contain Social Security numbers
- Protect download of files that contain protected health information
- Block download of files that have a sensitivity label of "very sensitive"
In such cases, files that are larger than 30 MB or that have more than 1 million characters aren't scanned. These files are treated according to the Always apply the selected action even if the data cannot be scanned policy setting.
The following table lists more examples of files that are and aren't scanned:
| File description | Scanned |
|---|---|
| A TXT file, 1-MB size and 1 million characters | Yes |
| A TXT file, 2-MB size and 2 million characters | No |
| A Word file composed of images and text, 4-MB size and 400K characters | Yes |
| A Word file composed of images and text, 4-MB size and 2 million characters | No |
| A Word file composed of images and text, 40-MB size and 400K characters | No |
Files encrypted with sensitivity labels
For tenants that enable coauthoring for files encrypted with sensitivity labels, a session policy to block file upload/download that relies on label filters or file content will operate based on the Always apply the selected action even if data cannot be scanned policy setting.
For example, assume that a session policy is configured to prevent downloading files that contain credit card numbers and is set to Always apply the selected action even if data cannot be scanned. Any file with an encrypted sensitivity label is blocked from downloading, regardless of its content.
External B2B users in Teams
Session policies don't protect external business-to-business (B2B) collaboration users in Microsoft Teams applications.
Limitations for sessions that the reverse proxy serves
The following limitations apply only on sessions that the reverse proxy serves. Users of Microsoft Edge can benefit from in-browser protection instead of using the reverse proxy, so these limitations don't affect them.
Built-in app and browser plug-in limitations
Conditional Access app control in Defender for Cloud Apps modifies underlying application code. It doesn't currently support built-in apps or browser extensions.
As an administrator, you might want to define default system behavior for when a policy can't be enforced. You can choose to either allow access or totally block it.
Context loss limitations
In the following applications, we encountered scenarios where browsing to a link might result in loss of the link's full path. Typically, the user lands on the home page of the app.
- ArcGIS
- GitHub
- Microsoft Power Automate
- Microsoft Power Apps
- Workplace from Meta
- ServiceNow
- Workday
File upload limitations
If you apply a session policy to block or monitor the upload of sensitive files, the user's attempts to upload files or folders by using a drag-and-drop operation block the complete list of files and folders in the following scenarios:
- A folder that contains at least one file and at least one subfolder
- A folder that contains multiple subfolders
- A selection of at least one file and at least one folder
- A selection of multiple folders
The following table lists example results when you define the Block upload of files that contain personal data to OneDrive policy:
| Scenario | Result |
|---|---|
| A user tries to upload a selection of 200 nonsensitive files by using a drag-and-drop operation. | Files are blocked. |
| A user tries to upload a selection of 200 files by using the file upload dialog. Some are sensitive, and some aren't. | Nonsensitive files are uploaded. Sensitive files are blocked. |
| A user tries to upload a selection of 200 files by using a drag-and-drop operation. Some are sensitive, and some aren't. | The full set of files is blocked. |