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Apple macOS / iOS UIFoundation Vulnerability

Medium

Synopsis

An issue exists with the NSAttributedString functionality in UIFoundation, particularly when creating objects that abstract the private functionality for NSHTMLReader. When creating NSAttributedString objects containing special formatting for URLs, if it is loaded into a container such as a tableview cell that has not been properly rendered or initialized, the application or service will crash. For example, when NSHTMLReader calls _loadUsingWebkit prior to a tableview cell being fully initialized, the application will crash. As a proof-of-concept, the flaw can be demonstrated locally (safely and recoverable) with the latest version of Notes.app. 1. Open Notes.app 2. Create a new note 3. Copy a URL from a popular web browser or an editor that will copy attributed data to the pasteboard. 4. In the new note, create a table view. 5. In the second row, attempt to paste URL. 6. The application will crash. Please note, Notes.app is being used for demonstration purposes. This is not just a flaw within Notes.app, it is a flaw within UIFoundation. All applications or services using or relying on this functionality are at risk. The primary impact here is a denial of service of the service or application affected, which could result in annoyance, loss of data, or inability to use the application. While the most likely scenario in cases such as this is simply denial-of-service oriented, it is theoretically possible that if developers handle the exception thrown here in some non-default way, other unpredictable circumstances may arise. As we do not have a proof-of-concept for that claim, we've decided to give this a CVSSv2 vector of (AV:N/AC:L/Au:N/C:N/I:N/A). Apple has rejected this bug report as having no security impact. While we understand their point-of-view, we would like to make others aware of the possible issues when developing using this functionality.

Solution

There is no fix available for this issue. We recommend developers rely on other existing functionality in alternative libraries if they are concerned about this issue.

Disclosure Timeline

July 17, 2019 - Initial Discovery.
July 22 2019 - Reported to Apple.
July 30, 2019 - Requested status update.
August 1, 2019 - Apple requests clarification.
August 2, 2019 - Tenable responds needing more information regarding what was unclear.
August 5, 2019 - Apple requests remote PoC.
August 7, 2019 - Tenable states that shouldn't be necessary.
August 8, 2019 - Apple states that this does not appear to have security implications, but will forward it to appropriate team for further investigation.

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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