CVE-2021-40927 in Spotify-for-Alfred
Summary
by MITRE • 10/02/2021
Cross-site scripting (XSS) vulnerability in callback.php in Spotify-for-Alfred 0.13.9 and below allows remote attackers to inject arbitrary web script or HTML via the error parameter.
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Analysis
by VulDB Data Team • 10/08/2021
The vulnerability identified as CVE-2021-40927 represents a critical cross-site scripting flaw within the Spotify-for-Alfred application version 0.13.9 and earlier. This issue manifests in the callback.php script which processes error parameters without adequate input sanitization or output encoding mechanisms. The vulnerability stems from the application's failure to properly validate and escape user-supplied data before incorporating it into web responses, creating an avenue for malicious actors to execute arbitrary JavaScript code within the context of a victim's browser session.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious payload containing script code within the error parameter of the callback.php endpoint. When the vulnerable application processes this parameter and renders it in the web interface without proper sanitization, the injected JavaScript executes in the victim's browser with the privileges of the affected user. This flaw operates under the Common Weakness Enumeration classification of CWE-79 - Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly escape or encode user input that gets reflected back to web clients. The vulnerability's impact is amplified by the fact that it affects a desktop application that interfaces with web services, creating a potential attack surface that bridges local application functionality with remote web-based exploitation vectors.
The operational implications of this XSS vulnerability extend beyond simple script injection, as it can enable attackers to perform session hijacking, steal sensitive user information, manipulate web application functionality, or redirect users to malicious websites. In the context of Spotify-for-Alfred, which integrates with the Spotify web service and potentially handles user authentication tokens or personal data, this vulnerability could allow attackers to access user accounts or compromise the integrity of the application's data handling processes. The attack requires minimal user interaction beyond visiting a malicious link or triggering the vulnerable callback mechanism, making it particularly dangerous in phishing scenarios or when users are unknowingly exposed to compromised content through social engineering tactics.
Mitigation strategies for this vulnerability should focus on implementing comprehensive input validation and output encoding mechanisms throughout the application's data flow. The primary remediation involves sanitizing all user-supplied input, particularly parameters like error messages, before they are processed or rendered in web contexts. This approach aligns with the ATT&CK framework's technique T1059.007 - Command and Scripting Interpreter: JavaScript, which emphasizes the importance of preventing malicious code execution through proper input handling. Application developers should implement proper HTML escaping routines for all dynamic content, utilize Content Security Policy headers to limit script execution, and consider implementing secure coding practices such as input whitelisting and parameterized queries. Additionally, users should be encouraged to update to the latest version of Spotify-for-Alfred where this vulnerability has been addressed through proper input sanitization and output encoding mechanisms.