CVE-2021-44025 in RoundCube
Summary
by MITRE • 11/19/2021
Roundcube before 1.3.17 and 1.4.x before 1.4.12 is prone to XSS in handling an attachment's filename extension when displaying a MIME type warning message.
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Analysis
by VulDB Data Team • 11/22/2021
This vulnerability exists in Roundcube webmail applications prior to versions 1.3.17 and 1.4.12, representing a cross-site scripting flaw that manifests when the application processes attachment filename extensions during MIME type warning displays. The security issue stems from insufficient input sanitization mechanisms that fail to properly escape or validate user-supplied data before incorporating it into dynamic HTML content. When a user encounters a file attachment with a potentially malicious filename extension, the application generates a warning message that includes the problematic filename without adequate sanitization, creating an avenue for attackers to inject malicious scripts. This vulnerability aligns with CWE-79, which specifically addresses cross-site scripting weaknesses in web applications, and demonstrates how improper output encoding can lead to unauthorized code execution in user browsers. The flaw operates at the application layer and directly impacts the integrity of the web interface's security model.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious filename extension that contains script tags or other malicious code within the attachment's file extension portion. During normal operation, when Roundcube displays a warning message about potential MIME type mismatches, the application incorporates the unfiltered filename extension directly into the HTML output. This creates a scenario where a user's browser executes the injected JavaScript code when rendering the warning message, potentially leading to session hijacking, data theft, or further compromise of the victim's browser environment. The vulnerability is particularly concerning because it leverages the legitimate warning functionality of the application to deliver malicious payloads, making it more difficult to detect and prevent through traditional security measures.
The operational impact of CVE-2021-44025 extends beyond simple script execution, as it can enable attackers to perform actions such as stealing user credentials, accessing sensitive email content, or redirecting users to malicious domains. The vulnerability affects both the 1.3.x and 1.4.x release lines of Roundcube, indicating it was present across multiple versions and likely persisted due to fundamental flaws in the input handling architecture. This issue falls under the ATT&CK technique T1059.007 for command and scripting interpreter, specifically targeting the execution of JavaScript within user browsers through web application vulnerabilities. The attack vector typically involves social engineering where users are tricked into downloading or opening attachments with maliciously crafted extensions, making it particularly dangerous in enterprise environments where email remains a primary attack surface.
Mitigation strategies for this vulnerability center on implementing proper input validation and output encoding mechanisms throughout the application's codebase. Organizations should immediately upgrade to Roundcube versions 1.3.17 or 1.4.12, which contain the necessary patches to address the XSS flaw. Additionally, administrators should implement content security policies that restrict script execution within the webmail interface and establish proper input sanitization routines that validate filename extensions against known safe patterns. The remediation process should include thorough code reviews focusing on all areas where user-supplied data is incorporated into HTML output, particularly warning messages and file handling operations. Security teams should also consider implementing web application firewalls that can detect and block suspicious patterns in attachment-related requests, while monitoring for anomalous file extension patterns that might indicate exploitation attempts.