whatsapp

WhatsApp for Android Retains Deleted Contacts Locally

nightwatchcyber Advisories, Research ,

Summary

WhatApp for Android retains contact info locally after contacts get deleted. This would allow an attacker with physical access to the device to check if the WhatsApp user had interactions with specific contacts, even though they have been deleted.

Vulnerability Details

When a contact is deleted on WhatsApp, their information about security code changes is retained (while the chat content is not). The only way to get rid of that is to select “Clear Chat” for the contact before deleting it. Even deleting the chat itself doesn’t do it unless the “Clear Chat” operation is done first. The “security code change notifications” option must be enabled in order for this to work.

Someone getting access to the user’s device can figure out whether they ever chatted with specific contacts, even if those contacts and their chats are no longer on the device. This is a privacy issue – especially for people like journalists and those living in dangerous countries.

Since WhatsApp uses Android’s contact app for contact information but supports chats with numbers that aren’t contacts, our theory is that the application retains information about security code changes even for contacts no longer on the device. There seems to be a discrepancy between how the “Clear chat” option and “Delete Chat” options are implemented in the application, with the first option deleting security notification data.

To reproduce:

  1. Delete a chat with a contact that had security code changes before.
  2. Delete the contact from the device via the Android Contacts app.
  3. Re-add contact to the device via the Android Contacts app.
  4. Start a new chat in WhatsApp with that contact but do not send any messages.
  5. Observe that security code changes are listed with dates in the chat.
  6. Select “Clear Chat” to remove the security code changes, and repeat sterps 1-4. Observe that the security code changes no longer appear.

Tested on WhatsApp for Android, app version 2.21.20.20, running on Android 12.

Vendor Response

We haven’t retested on a more recent version but our recommendation to users is to use the “Clear Chat” option in order to prevent this.

The vendor will not be fixing this issue, here is their response:

As part of the attack scenario you describe getting access to a person’s WhatsApp account to obtain private data, as you mention yourself, people do have a way to remove these messages from their account, if a bad actor gets access to their WhatsApp account prior to that person deleting that information then they will be able to view this information. As such, we are closing this report.

References

CWE: CWE-212 – Improper Removal of Sensitive Information Before Storage or Transfer

Facebook # 10102482597361835

Timeline

2021-10-24: Initial report sent to the vendor, report ID assigned
2021-10-27: Vendor asks for more info, additional info and screenshots sent
2021-11-03: Vendor sent interim status report, still investigating
2021-11-09: Vendor rejects the vulnerability and closes the report
2021-12-30: Public disclosure

Brief Notes on WhatsApp Link Previews

nightwatchcyber Research

(All testing was performed using WhatsApp for Android v2.20.201.20 and WhatsApp Web)

Introduction

Recently, we have been looking into possible security issues around how WhatsApp parses and displays preview information about hyperlinks. Basically, WhatsApp will parse some basic information from a hyperlink and display it within the body of a chat. Based on our sleuthing, it appears to be parsed from various elements in the original HTML. For Google, it looks like this:

Parsing code

This appears to be parsed from various meta tags within the original site as per the code snippet below. If those are not present, it will use the “title” tag instead. Here is some of the parsing code:

Additional Details on HTML Retrieval

From testing and review of logs, it appears that the actual call to retrieve the site happens on the Android client. There are also some additional interesting points:

  • The retrieval is cached on the client
  • If WhatsApp Web is used, the retrieval still happens on the mobile phone with the parsed results transferred to the Web version
  • If a link is forwarded, posted into a chat or group, there is no additional retrieval that happens. Instead, the parsed preview is transmitted along with the link

Here is the actual snippet of decompiled code doing the retrieval:

Future Areas for Research

We plan to research the actual parsing and retrieval of the HTML with the eye towards trying to see if any of the parsing code can be manipulated to inject content into the client or the Web version. For things like images and videos, there is potential for exploiting the underlying native code.

Advisory: WhatsApp for Android Privacy Issues with Handling of Media Files [CVE-2017-8769]

nightwatchcyber Advisories , ,

Summary

WhatsApp Messenger for Android does not delete sent and received files from the SD card on the device when chats are cleared, deleted or the application is uninstalled from the device. Additionally, the application stores sent and received files in the SD card without encryption where they are accessible to any applications with storage permissions.

The vendor (Facebook) doesn’t consider these to be security issues and does not plan to fix them. MITRE has assigned CVE-2017-8769 for these issues. It is also unclear whether platforms other than Android are affected.

[UPDATE: 09/06/2017 – a recent update to WhatsApp for Android now displays an option to delete media files when deleting chats and that option is checked by default. The change to the UI mitigates the issues discussed in this advisory. Users are encouraged to update to v2.16.323 or later.]

[UPDATE: 12/05/2017 – the checkbox to delete media files when deleting chats doesn’t always work. Users are encouraged to delete the WhatsApp directory on the SD card using a file manager to make sure all media files are removed and be aware of issues with erasing flash memory in general. Facebook has refused to acknowledge this as a security issue and has not plans to fix it.]

Background

WhatsApp Messenger is a popular cross-platform communication tool that allows users to send and receive messages without using more expensive protocols like SMS. Additionally the application allows sending and receiving of files including audio, contacts, images, videos and arbitrary documents. It is estimated that WhatsApp has over 1 billion active users and it is owned by Facebook, which also operates the largest social networking site in the world.

One of the main selling points that WhatsApp makes is their commitment to user privacy which revolves around the implementation of end-to-end encryption via the Signal protocol originally developed by Open Whisper Systems. This encryption makes it impossible for Facebook to monitor and capture message traffic flowing between users. In some extreme cases, Facebook executives have been placed in jail for the failure to allow access to messaging data when requested by governments.

Because of the high expectation of privacy by WhatsApp user, it is important that the security of the application on the device is also properly implemented. In regards to messages, WhatsApp stores them in encrypted database but it fails to do the same for files. WhatsApp also does not clear files received or sent by the user when the chats are cleared. This can result in user data being leaked or stolen by malicious applications, law enforcement during illegal searches or unwanted actors having access to the device (“evil maid scenario”).

Vulnerability Details

As mentioned above, WhatsApp has ability to send and receive files in addition to regular messages. This functionality includes arbitrary documents from the file system, contacts, location information, and various type of multimedia files including two separate audio formats (voice notes and recordings), images and videos. There is also more recent functionality around “status” images which disappear after 24 hours. In order for WhatsApp to access the SD card, users must grant storage permissions but in practice most users do so in order to be able to exchange files.

In our research, we have found that WhatsApp for Android stores these files on the SD card where they are accessible to other applications and does not delete them when chats are cleared, deleted or the application is uninstalled. Both sent and received files are retained. They are retained on the SD card in the following folder:

  • /WhatsApp/Media/

We have observed that the following file types are retained and not deleted:

  • /WhatsApp/Media/.Statuses/
  • /WhatsApp/Media/WhatsApp Audio/
  • /WhatsApp/Media/WhatsApp Documents/
  • /WhatsApp/Media/WhatsApp Images/
  • /WhatsApp/Media/WhatsApp Video/
  • /WhatsApp/Media/WhatsApp Voice Notes/

Screenshot_20170512-000800

To replicate the issue:

  1. Install WhatsApp for Android.
  2. Login and exchange messages with another user that contain any of the file type listed above.
  3. Then, install any file manager for Android.
  4. Navigate to the SD card, and observe the files sent and received being located in the directories described above.

As the next step, try to delete a chat by tapping on the chat, holding until the delete option comes up. Delete the chat, and go back to the file manager to check.

As the next step, try going to “Settings”, “Chats”, “Chat History” and selecting either “Clear all chats” or “Delete all chats”. Go back to the file manager and observe the media files still being present.

Screenshot_20170512-000723

As the next step, uninstall WhatsApp. Go back to the file manager, and observe the media files still being there.

All testing was done on Android 7, and WhatsApp Messenger v2.17.146. It is unclear whether other platforms are affected.

Vendor Response and Mitigation Steps

The vendor (Facebook) doesn’t consider these to be security issues and has no plans to fix them. Vendor response is as follows:

Thanks again for your report. We contacted the WhatsApp team about your report, and they confirmed that the behavior you describe is intentional. They designed the Android app to optimize for the storage space available on devices and allow media in WhatsApp to be visible in other apps like the Google Photos gallery. WhatsApp doesn’t assume that clearing the chat means clearing the media files as well. While the behavior might change in the future, we currently don’t have any plans to do so.

The vendor also noted that on Windows Phone, there is a setting that stops the application from saving media files that are received by the user.

It is recommended that users regularly check the folders listed above on the SD card and empty them as needed. For those users who desire higher security, it may be prudent to reformat or encrypt the SD card, or destroy the SD card if needed in order to delete these files.

[UPDATE: 09/06/2017] – a recent update to WhatsApp for Android now displays an option to delete media files when deleting chats and that option is checked by default. The change to the UI mitigates the issues discussed in this advisory. Users are encouraged to update to v2.16.323 or later.

New response from the vendor:

>> We published on this back in May. It looks like that the most recent version of WhatsApp for Android adds a mitigation for this issue. Can you confirm?

Yes, The WhatsApp team indeed added a background job to clear media.

Screenshots of the new UI:

Screenshot_20170906-164803whatsapp2

[UPDATE: 12/05/2017 – the checkbox to delete media files when deleting chats doesn’t always work. Users are encouraged to delete the WhatsApp directory on the SD card using a file manager to make sure all media files are removed and be aware of issues with erasing flash memory in general. Facebook has refused to acknowledge this as a security issue and has not plans to fix it.]

New response from the vendor:

Thank you clarifying more. According to the post you linked to, Facebook had informed that the CVE-2017-8769 was not considered a security risk. Since what you describe doesn’t appear to be a security vulnerability, you can report a general software bug by contacting WhatsApp at: [email protected]

References

CVE ID: CVE-2017-8769
CWE IDs: CWE-359 (“Exposure of Private Information”)
Facebook security reference # 10101277738643365

Credits

Advisory written by Yakov Shafranovich.

Timeline

2017-04-09: Initial report to Facebook
2017-04-14: Email exchange with the vendor
2017-04-20: Email exchange with the vendor
2017-04-03: Email exchange with the vendor
2017-05-09: Email exchange with the vendor
2017-05-16: Email exchange with the vendor
2017-05-17: Email exchange with the vendor
2017-05-17: Public disclosure
2017-09-06: Updated with details of the new UI changes in the Android app that mitigate these issues
2017-09-11: Email exchange with the vendor

2017-12-05: Followup exchange with the vendor