CVE-2018-3986 in Telegram
Summary
by MITRE
An exploitable information disclosure vulnerability exists in the "Secret Chats" functionality of the Telegram Android messaging application version 4.9.0. The "Secret Chats" functionality allows a user to delete all traces of a chat, either by using a time trigger or by direct request. There is a bug in this functionality that leaves behind photos taken and shared on the secret chats, even after the chats are deleted. These photos will be stored in the device and accessible to all applications installed on the Android device.
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Analysis
by VulDB Data Team • 06/23/2023
The vulnerability described in CVE-2018-3986 represents a critical information disclosure flaw within Telegram's Secret Chats implementation on Android devices. This security weakness specifically affects version 4.9.0 of the messaging application and fundamentally undermines the privacy assurances that users expect from encrypted communication channels. The vulnerability exposes sensitive visual data that should have been completely eliminated from device storage following chat deletion, creating a persistent security risk that extends beyond the intended scope of the application's privacy features.
The technical implementation flaw resides in the Secret Chats functionality's cleanup mechanism, which fails to properly remove all associated media files from device storage when users initiate chat deletion. While the system correctly implements time-based and manual deletion triggers for chat conversations, the underlying file management process contains a critical oversight that allows image files to persist in the device's file system. This occurs despite the application's promise that secret chats should leave no trace of communication content, including multimedia files that were shared during the conversation. The persistence of these photos violates fundamental security principles and creates an unexpected data exposure channel.
The operational impact of this vulnerability extends beyond simple data retention issues and represents a significant breach of user privacy expectations. Once photos remain accessible on the device, they become vulnerable to unauthorized access by malicious applications installed on the same Android device, as well as through potential exploitation by adversaries with physical device access. This creates a persistent threat vector where sensitive visual information shared through secret chats remains accessible to any application with appropriate file system permissions, effectively nullifying the privacy protections that users rely upon when engaging with the Secret Chats feature. The vulnerability particularly affects users who engage in sensitive communications where visual evidence might contain personal or confidential information.
From a cybersecurity perspective, this vulnerability aligns with CWE-200 (Information Exposure) and represents a failure in secure deletion practices that should have been implemented according to industry security standards. The flaw demonstrates inadequate input validation and output handling within the application's file management subsystem, where the deletion process does not adequately verify that all associated files have been properly removed from storage. This vulnerability also maps to ATT&CK technique T1070.004 (File Deletion) which emphasizes the importance of proper file cleanup mechanisms in maintaining system security and user privacy. The persistence of media files represents a failure in the principle of least privilege and proper resource management that should be enforced by the application's security architecture. Users who rely on Telegram's Secret Chats for sensitive communications may unknowingly expose their visual data to unauthorized access, creating potential risks for individuals and organizations that depend on secure communication channels. The vulnerability underscores the critical importance of comprehensive testing and validation of deletion mechanisms in privacy-focused applications, particularly those handling sensitive multimedia content that may contain personal or confidential information.