CVE-2016-1566 in Guacamole
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the file browser in Guacamole 0.9.8 and 0.9.9, when file transfer is enabled to a location shared by multiple users, allows remote authenticated users to inject arbitrary web script or HTML via a crafted filename. NOTE: this vulnerability was fixed in guacamole.war on 2016-01-13, but the version number was not changed.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/10/2020
The CVE-2016-1566 vulnerability represents a critical cross-site scripting flaw discovered in Apache Guacamole versions 0.9.8 and 0.9.9, specifically affecting the file browser functionality when file transfer capabilities are enabled across shared user locations. This vulnerability resides within the web-based interface of Guacamole, which serves as a clientless remote desktop gateway supporting various protocols including RDP, VNC, and SSH. The flaw manifests when multiple users access shared file locations, creating an environment where malicious actors can exploit the lack of proper input sanitization in filename handling. The vulnerability is particularly concerning because it requires only authenticated access, meaning that any user with valid credentials within the system can potentially exploit this weakness to execute arbitrary web scripts or HTML code against other users.
The technical implementation of this vulnerability stems from insufficient validation and sanitization of user-provided filenames within the file browser component. When users upload or create files with maliciously crafted names containing script tags or other HTML elements, the application fails to properly escape or filter these inputs before rendering them in the browser context. This allows attackers to inject malicious code that executes in the context of other users' browsers, potentially leading to session hijacking, credential theft, or further exploitation of the compromised user sessions. The vulnerability specifically impacts the file transfer functionality that enables users to share files across different sessions and connections, making it particularly dangerous in multi-user environments where file sharing is a common operation. According to CWE standards, this vulnerability maps to CWE-79 which describes improper neutralization of input during web output, and the ATT&CK framework categorizes this under T1059.001 for command and scripting interpreter, specifically targeting web-based scripting execution.
The operational impact of CVE-2016-1566 extends beyond simple script injection, as it can enable attackers to establish persistent access within the Guacamole environment. Once an attacker successfully injects malicious code through a crafted filename, they can potentially steal session cookies, redirect users to malicious sites, or perform actions on behalf of other users with the same privileges. The vulnerability's persistence is enhanced by the fact that it affects shared file locations, meaning that a single malicious filename can impact multiple users simultaneously. Attackers can leverage this to create phishing campaigns, steal sensitive information from other authenticated users, or use the compromised sessions as stepping stones for further network exploration. The fact that this vulnerability was patched in the guacamole.war file on January 13, 2016, but the version number remained unchanged, created additional challenges for system administrators who needed to verify whether their installations were properly secured. Organizations running affected versions of Guacamole faced significant risk during the period when this vulnerability was publicly known, particularly in environments where file sharing was actively used across multiple user accounts. The vulnerability demonstrates the critical importance of proper input validation and output encoding in web applications, especially in multi-user systems where shared resources can become attack vectors. Security professionals should note that this vulnerability aligns with ATT&CK technique T1566.001 for credential access through web-based attacks, making it a significant concern for organizations implementing remote desktop solutions that rely on web interfaces.