CVE-2017-17533 in Tkabber
Summary
by MITRE
default.tcl in Tkabber 1.1 does not validate strings before launching the program specified by the BROWSER environment variable, which might allow remote attackers to conduct argument-injection attacks via a crafted URL.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2017-17533 resides within the default.tcl script of Tkabber version 1.1, a popular instant messaging client that utilizes the Tk graphical toolkit. This flaw represents a classic command injection vulnerability that arises from insufficient input validation mechanisms. The vulnerability specifically manifests when the application processes URLs through the BROWSER environment variable, creating an attack surface where malicious inputs can be executed as shell commands without proper sanitization or validation.
The technical implementation of this vulnerability stems from the application's failure to properly sanitize user-provided strings before incorporating them into system commands. When Tkabber processes a URL that contains maliciously crafted arguments, the default.tcl script directly passes these unvalidated inputs to the system shell through the BROWSER environment variable. This behavior aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and represents a fundamental flaw in input handling that allows attackers to inject arbitrary commands into the execution context.
The operational impact of this vulnerability extends beyond simple command execution, as it enables remote attackers to perform argument-injection attacks that can compromise the entire system. An attacker could craft a malicious URL containing shell metacharacters and special command separators that would be interpreted and executed by the underlying operating system when the BROWSER environment variable is invoked. This creates a persistent threat vector that can be exploited through various attack vectors including malicious chat messages, web links, or file transfers within the Tkabber environment, potentially allowing for complete system compromise.
From an attack framework perspective, this vulnerability maps to multiple ATT&CK techniques including T1059.001 for command and scripting interpreter and T1203 for Exploitation for Client Execution. The vulnerability's remote exploitation capability means that attackers do not require local access to the system, making it particularly dangerous in environments where users might interact with untrusted content. The attack chain typically involves crafting a malicious URL that includes shell command injection payloads, which are then processed by the vulnerable Tkabber application when users click on the links or interact with the content.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization mechanisms within the default.tcl script. The recommended approach includes implementing strict string validation that filters out special shell metacharacters and command separators before any processing occurs. Additionally, the application should utilize parameterized command execution where possible, ensuring that user inputs are treated as data rather than executable code. Organizations should also implement network-level protections including firewall rules that restrict access to potentially vulnerable services and conduct regular security assessments to identify similar input validation flaws in other components of the messaging infrastructure. The vulnerability underscores the critical importance of secure coding practices and input validation in client-side applications that interact with system-level commands through environment variables.