CVE-2023-26818: Telegram Privilege Escalation Vulnerability

CVE-2023-26818 Overview

CVE-2023-26818 is an Authorization Bypass vulnerability affecting Telegram for macOS versions 9.3.1 and 9.4.0. The vulnerability allows attackers to bypass macOS Transparency, Consent, and Control (TCC) protections to access restricted files, microphone, or video recording capabilities via the DYLD_INSERT_LIBRARIES environment variable injection technique.

Critical Impact

Attackers can leverage this vulnerability to gain unauthorized access to sensitive system resources including the microphone and camera, bypassing macOS privacy controls that normally require explicit user consent.

Affected Products

• Telegram for macOS version 9.3.1
• Telegram for macOS version 9.4.0

Discovery Timeline

• 2023-05-19 - CVE-2023-26818 published to NVD
• 2025-01-21 - Last updated in NVD database

Technical Details for CVE-2023-26818

Vulnerability Analysis

This vulnerability exploits a weakness in how Telegram for macOS handles dynamic library loading. The DYLD_INSERT_LIBRARIES environment variable is a macOS mechanism that allows injecting dynamic libraries into a process at load time. When combined with Telegram's existing TCC permissions for microphone and camera access, an attacker can inject malicious code that inherits these permissions.

The root issue stems from Telegram's failure to implement the hardened runtime with library validation, which would normally prevent unauthorized dynamic library injection. Since Telegram has already been granted TCC permissions by the user for legitimate functionality, injected code runs with the same privilege level and can access protected resources without triggering additional consent prompts.

Root Cause

The vulnerability exists due to Telegram for macOS lacking proper library validation enforcement in its hardened runtime configuration. Without the com.apple.security.cs.disable-library-validation entitlement properly restricted, the application accepts injected libraries through DYLD_INSERT_LIBRARIES. This is classified as CWE-863 (Incorrect Authorization), as the application fails to properly authorize which libraries can execute within its security context.

Attack Vector

The attack requires local access to the target system and exploits the dynamic library loading mechanism in macOS. An attacker creates a malicious dynamic library (dylib) that contains code to access protected resources. By setting the DYLD_INSERT_LIBRARIES environment variable to point to this malicious library and then launching Telegram, the injected code inherits Telegram's TCC permissions for microphone, camera, and file access.

The attack flow involves:

1. Creating a malicious dylib that accesses TCC-protected resources
2. Setting the DYLD_INSERT_LIBRARIES environment variable to the malicious library path
3. Launching Telegram, which loads the injected library
4. The malicious code executes with Telegram's TCC permissions, bypassing user consent dialogs

Technical details and proof-of-concept information are available in the CVE-2023-26818 analysis published by the security researcher.

Detection Methods for CVE-2023-26818

Indicators of Compromise

• Unusual DYLD_INSERT_LIBRARIES environment variable settings when Telegram is launched
• Unexpected dylib files in user-writable directories being loaded by Telegram
• Telegram process accessing microphone or camera at unexpected times
• Shell scripts or launch agents that set DYLD_INSERT_LIBRARIES before launching Telegram

Detection Strategies

• Monitor process creation events for Telegram launches that include DYLD_INSERT_LIBRARIES environment variables
• Implement file integrity monitoring on Telegram's application bundle and related directories
• Deploy endpoint detection rules that alert on dynamic library injection attempts targeting signed applications
• Analyze process memory for loaded libraries that don't match expected Telegram modules

Monitoring Recommendations

• Enable macOS Unified Logging and monitor for TCC bypass indicators
• Configure SentinelOne agents to detect and alert on DYLD_INSERT_LIBRARIES abuse patterns
• Monitor for unexpected microphone or camera access events associated with Telegram
• Audit launch agents and daemons for suspicious environment variable configurations

How to Mitigate CVE-2023-26818

Immediate Actions Required

• Update Telegram for macOS to the latest available version that addresses this vulnerability
• Review and audit TCC permissions granted to Telegram and revoke unnecessary access
• Implement application allow-listing to prevent unauthorized library loading
• Monitor endpoints for signs of exploitation using EDR solutions

Patch Information

Users should update to a patched version of Telegram for macOS. Check the official Telegram website for the latest security updates and version information. Ensure automatic updates are enabled to receive security patches promptly.

Workarounds

• Temporarily revoke TCC permissions (microphone, camera, file access) from Telegram until a patch is applied
• Use the App Store version of Telegram which has additional sandboxing protections
• Implement endpoint protection that monitors for DYLD_INSERT_LIBRARIES abuse
• Consider running Telegram in a virtualized or sandboxed environment for sensitive workflows

# Check Telegram's TCC permissions and revoke if necessary
# Reset TCC permissions for Telegram (requires SIP disabled or MDM)
tccutil reset Microphone com.telegram.desktop
tccutil reset Camera com.telegram.desktop

# Verify hardened runtime status
codesign -dv --verbose=4 /Applications/Telegram.app 2>&1 | grep -i runtime