The Telegram secure messaging application was found to breach users’ privacy by failing to properly remove images from a device’s local storage when the sender selects to delete them for all recipients.
The option was meant to provide users with the possibility to delete messages that were sent by mistake or genuinely to any recipient. By deleting erroneously sent messages, the app helped preserve users’ privacy, though it appears that the feature didn’t always work as intended.
What a security researcher with InputZero discovered was that Telegram would save received images to the internal storage of the recipient’s device, at the ‘/Telegram/Telegram Images/’ path.
Images stored there would not be removed from the folder when the user selected the option to remove the image from the conversation for all participants, which resulted in unintentional recipients still being able to access the images by navigating to /Telegram/Telegram Images/.
What’s more, the vulnerability would also manifest for the Telegram “supergroups.” Thus, media shared to those groups would remain on the devices of all recipients.
Telegram, however, requests and takes ‘read/write/modify’ permissions for the USB storage, meaning that it should be able to remove confidential photos from local storage when the sender triggers the process.
The security researcher, who published a video proof-of-concept, says the issue was found in version 5.10.0 (1684) of Telegram for Android. The iOS and Windows versions of the application were not tested, but could be vulnerable.
The researcher reported the vulnerability to Telegram, which was quick to issue a patch. The company also awarded the researcher a €2,500 ($2,760) bounty for the finding.
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