CVE-2026-74999 in Roundcube
Summary
by MITRE • 08/17/2026
In Roundcube Webmail before 1.6.18 and 1.7.x before 1.7.3, the "Add to address book" action was subject to stored XSS.
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Analysis
by VulDB Data Team • 08/17/2026
The vulnerability identified in Roundcube Webmail versions prior to 1.6.18 and 1.7.x prior to 1.7.3 represents a critical security flaw within the application's contact management subsystem. Specifically, the functionality designed to allow users to save email addresses or names into their personal address book fails to adequately sanitize user-supplied input before storing it in the backend database. This lack of proper validation and encoding allows an attacker to inject malicious JavaScript code directly into the stored data fields associated with a contact entry. When this vulnerability is exploited, it falls under the category of Stored Cross-Site Scripting, also known as Persistent XSS, where the injected script remains on the server until retrieved by another user or even the victim themselves upon viewing their address book.
From a technical perspective, the flaw resides in how Roundcube processes and renders contact information within its web interface. When an administrator or any authenticated user adds a new entry to the address book, the application accepts various fields such as name, email, and notes without sufficiently stripping out executable script tags or event handlers like onerror or onload. Consequently, when these entries are displayed in subsequent requests, typically through standard HTML rendering mechanisms that do not enforce strict content security policies against user-generated content, the browser interprets the injected code as legitimate scripts belonging to the application domain. This behavior aligns with CWE-79, which classifies Improper Neutralization of Input During Web Page Generation as a fundamental weakness in web applications lacking robust input validation and output encoding strategies.
The operational impact of this vulnerability is severe due to its persistent nature unlike reflected XSS where the payload must be delivered via a link stored XSS persists on the server side. An attacker who gains access to create address book entries can plant payloads that execute every time any user views their contacts list. This enables session hijacking, credential theft through keyloggers embedded in the script, or redirection of users to phishing sites designed to mimic Roundcube login pages. Furthermore because the attack vector is integrated into a core feature used frequently by administrators and power users the likelihood of successful exploitation increases significantly as victims are more likely to interact with their address book regularly without suspecting malicious content within trusted application interfaces.
This vulnerability maps directly to MITRE ATT&CK technique T1059 which covers Command and Scripting Interpretation specifically JavaScript execution in a browser context through stored payloads it also relates to T1189 Drive-by Compromise if the script triggers automatic downloads or exploits other browser vulnerabilities upon loading. The persistence of the payload means that even after the initial attacker has left, the threat remains active within the system requiring manual intervention to remove infected records from the database and update the application software.
Mitigation strategies primarily involve upgrading Roundcube Webmail to version 1.6.18 or later for stable branches or 1.7.3 and above for development branches where these input sanitization issues have been addressed through improved encoding practices and stricter validation rules on all user inputs destined for storage. In environments where immediate patching is not feasible administrators should implement Web Application Firewall rules that detect and block common XSS patterns in POST requests targeting address book endpoints although this is a less reliable defense than proper code remediation additionally enforcing strict Content Security Policy headers can help mitigate the impact by restricting script execution to trusted sources thereby preventing unauthorized scripts injected via stored vectors from running even if they are successfully rendered.