CVE-2026-54432 in Roundcube
Summary
by MITRE • 07/14/2026
Roundcube Webmail before 1.6.17 and 1.7.x before 1.7.2 allows Stored Cross-Site Scripting (XSS). The issue occurs because the attachment MIME type is not properly escaped on the attachment-validation warning page.
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Analysis
by VulDB Data Team • 07/15/2026
This vulnerability represents a critical stored cross-site scripting flaw in Roundcube Webmail that affects versions prior to 1.6.17 and 1.7.x before 1.7.2. The security issue stems from insufficient input validation and output escaping mechanisms within the attachment handling system, specifically when displaying warning messages about invalid MIME types during attachment validation processes. The flaw allows attackers to inject malicious javascript code through carefully crafted attachment filenames that contain unescaped special characters, which are then rendered in the warning page without proper sanitization.
The technical implementation of this vulnerability occurs when Roundcube processes email attachments and encounters files with suspicious or unsupported MIME type declarations. During the validation process, the system displays a warning message to users indicating the attachment has an invalid or potentially dangerous MIME type. However, the application fails to properly escape the MIME type information before rendering it in the web interface, creating an XSS vector that can be exploited by malicious actors. This represents a classic stored XSS vulnerability where the malicious payload is persisted in the application's state and executed when other users view the warning page.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with a potential foothold for more sophisticated attacks within the email environment. Once successfully exploited, an attacker could execute arbitrary javascript code in the context of authenticated users' browsers, potentially leading to session hijacking, data exfiltration, or privilege escalation within the webmail application. The vulnerability is particularly concerning in enterprise environments where Roundcube serves as a corporate email solution, as it could enable attackers to access sensitive organizational communications and potentially compromise multiple user accounts simultaneously.
Organizations utilizing affected Roundcube versions should prioritize immediate patching to address this security gap. The recommended mitigation involves upgrading to Roundcube Webmail version 1.6.17 or 1.7.2, which includes proper input sanitization and output escaping mechanisms for attachment MIME type validation warnings. Security teams should also implement additional monitoring for suspicious attachment uploads and consider implementing web application firewalls that can detect and block known XSS attack patterns targeting this specific vulnerability class. This issue aligns with CWE-79 (Cross-site Scripting) and maps to ATT&CK technique T1566.001 (Phishing via Service) as attackers could use this vulnerability to deliver malicious payloads through email attachments, potentially bypassing traditional email security controls that focus on content filtering rather than client-side vulnerabilities.
The root cause of this vulnerability demonstrates a common security pattern where applications fail to properly separate data from code execution contexts, particularly in user-facing warning messages that display system-generated information. This type of flaw underscores the importance of implementing comprehensive input validation and output encoding practices throughout web applications, especially when dealing with user-provided data that may contain special characters or control sequences. Organizations should conduct thorough vulnerability assessments to identify similar issues in other components where user input is displayed without proper sanitization, as this represents a systemic security weakness that could affect multiple application modules beyond just attachment handling functionality.