CVE-2020-15864 in CloudShell
Summary
by MITRE • 01/18/2021
An issue was discovered in Quali CloudShell 9.3. An XSS vulnerability in the login page allows an attacker to craft a URL, with a constructor.constructor substring in the username field, that executes a payload when the user visits the /Account/Login page.
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Analysis
by VulDB Data Team • 02/15/2021
The vulnerability identified as CVE-2020-15864 represents a critical cross-site scripting flaw within Quali CloudShell version 9.3 that specifically targets the authentication interface. This issue arises from inadequate input validation and sanitization mechanisms implemented in the login page's username field processing. The flaw enables attackers to inject malicious JavaScript code through crafted URLs that contain the substring constructor.constructor, which when processed by the vulnerable application can lead to arbitrary code execution within the context of the victim's browser session.
The technical exploitation of this vulnerability stems from the application's failure to properly sanitize user input before rendering it in the web interface. When a user navigates to the /Account/Login page with a maliciously constructed URL containing the specific payload pattern, the application processes the username parameter without adequate security controls. This vulnerability directly maps to CWE-79 which defines cross-site scripting as a weakness where untrusted data is sent to a web browser without proper validation or escaping. The attack vector leverages the JavaScript constructor function's ability to dynamically create functions, making it particularly dangerous as it can bypass traditional security measures designed to block simple script tags or other obvious malicious payloads.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking, as it provides attackers with a persistent means of executing malicious code within the victim's browser context. Once a user clicks on the malicious URL, the attacker can potentially steal session cookies, perform actions on behalf of the authenticated user, or redirect the victim to malicious sites. This vulnerability is particularly concerning in enterprise environments where CloudShell is used for infrastructure management and orchestration, as successful exploitation could lead to unauthorized access to critical cloud resources and potentially escalate to full system compromise. The vulnerability affects the authentication phase of the application, making it a prime target for initial access attacks and privilege escalation attempts.
Mitigation strategies for CVE-2020-15864 should focus on implementing comprehensive input validation and output encoding mechanisms throughout the application's user input handling processes. Organizations should immediately apply the vendor-provided patches or updates to resolve the vulnerability. Additional protective measures include implementing strict Content Security Policy headers, sanitizing all user inputs before processing, and conducting regular security assessments of authentication interfaces. The vulnerability also highlights the importance of following secure coding practices that align with OWASP Top Ten recommendations, particularly those addressing input validation and output encoding. Organizations should consider implementing web application firewalls to detect and block similar attack patterns and establish monitoring protocols to identify potential exploitation attempts. The ATT&CK framework categorizes this as a web application attack vector under the initial access phase, emphasizing the need for layered security controls to prevent unauthorized access through authentication interfaces.