CVE-2019-9535 in iTerm2
Summary
by MITRE
A vulnerability exists in the way that iTerm2 integrates with tmux's control mode, which may allow an attacker to execute arbitrary commands by providing malicious output to the terminal. This affects versions of iTerm2 up to and including 3.3.5. This vulnerability may allow an attacker to execute arbitrary commands on their victim's computer by providing malicious output to the terminal. It could be exploited using command-line utilities that print attacker-controlled content.
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Analysis
by VulDB Data Team • 09/30/2020
The vulnerability identified as CVE-2019-9535 represents a critical security flaw in iTerm2 terminal emulator software that specifically impacts versions up to and including 3.3.5. This issue arises from the integration between iTerm2 and tmux's control mode functionality, creating a pathway for remote code execution through seemingly benign terminal output manipulation. The flaw demonstrates how terminal emulators can become attack vectors when they fail to properly sanitize input from integrated terminal multiplexer applications, particularly when these applications operate in control mode where they communicate with the terminal through escape sequences and control codes.
The technical implementation of this vulnerability stems from insufficient input validation within iTerm2's handling of tmux control mode communications. When iTerm2 processes output from tmux in control mode, it fails to properly sanitize or validate the escape sequences and control codes that tmux may send to the terminal. This lack of proper sanitization allows an attacker to craft malicious output that contains specially formatted escape sequences which iTerm2 interprets as commands rather than mere display instructions. The vulnerability specifically exploits the way iTerm2 processes these control sequences, treating them as executable commands instead of simple formatting instructions, thereby creating a command injection scenario. This flaw aligns with CWE-74, which describes improper neutralization of special elements in output that could be interpreted as commands by a target system, and represents a classic case of command injection through terminal interface manipulation.
The operational impact of CVE-2019-9535 extends beyond simple privilege escalation to encompass full system compromise through a sophisticated attack vector that leverages the trusted relationship between terminal applications and their integrated components. An attacker could exploit this vulnerability by providing malicious output to a victim's terminal session through command-line utilities that print attacker-controlled content, effectively bypassing traditional security boundaries. This attack scenario becomes particularly dangerous because it operates at the terminal level, where users typically have elevated privileges and where the attack surface includes access to system resources, network connections, and potentially sensitive data. The vulnerability allows for arbitrary code execution on the victim's computer without requiring any special privileges or user interaction beyond the normal operation of terminal applications, making it a significant concern for security-conscious environments.
Mitigation strategies for CVE-2019-9535 must address both the immediate vulnerability and broader security practices around terminal application usage. The most direct solution involves upgrading to iTerm2 versions that have patched this vulnerability, specifically versions beyond 3.3.5 where the input sanitization issues have been resolved. Organizations should implement comprehensive patch management procedures to ensure all terminal emulators are kept up to date, particularly in environments where multiple users may be exposed to potentially malicious content. Additionally, security teams should consider implementing network-level controls to monitor and restrict the types of escape sequences that can be transmitted through terminal sessions, particularly in shared or public computing environments. The vulnerability demonstrates the importance of validating all input from integrated applications, and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: PowerShell, highlighting the need for proper input validation across all terminal interfaces. Security monitoring should include detection of unusual escape sequence patterns that may indicate exploitation attempts, while system administrators should consider implementing terminal session logging to track potentially malicious activity. The incident also underscores the necessity of adhering to secure coding practices that prevent command injection vulnerabilities in terminal applications, particularly those that process external input through control mode interfaces.