CVE-2026-54433 in Roundcube
Summary
by MITRE • 07/14/2026
In Roundcube Webmail before 1.6.17 and 1.7.x before 1.7.2, there is Stored Cross-Site Scripting (XSS) via a crafted plain-text email message. The attacker-controlled JavaScript executes within the victim's authenticated session simply by opening or previewing the message (zero-click).
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Analysis
by VulDB Data Team • 07/14/2026
The vulnerability in Roundcube Webmail represents a critical stored cross-site scripting flaw that affects versions prior to 1.6.17 and 1.7.x before 1.7.2. This security weakness allows attackers to inject malicious javascript code into email messages that are subsequently executed when victims view or preview these messages within the webmail interface. The vulnerability operates as a stored XSS attack because the malicious payload is permanently stored on the server and persists until explicitly removed, making it particularly dangerous for widespread exploitation. The attack requires no interaction from the victim beyond simply opening or previewing the malicious email, which classifies it as a zero-click exploit that can be delivered through various means including phishing campaigns or compromised email accounts.
The technical implementation of this vulnerability stems from insufficient input validation and output sanitization within Roundcube's email handling mechanisms. When users open or preview email messages containing crafted javascript payloads, the application fails to properly escape or filter special characters that could be interpreted as executable code by web browsers. This occurs specifically in the rendering process where plain-text email content is displayed without adequate security measures to prevent script execution. The flaw resides in the application's failure to implement proper content sanitization routines that would neutralize potentially dangerous input before it reaches the browser environment, creating an attack surface that directly violates fundamental secure coding practices.
The operational impact of this vulnerability is severe as it enables attackers to execute arbitrary javascript code within the context of authenticated user sessions. This means compromised users could be subjected to session hijacking, credential theft, data exfiltration, or redirection to malicious websites without any user interaction beyond viewing the email. The zero-click nature of exploitation makes this particularly dangerous for large organizations where employees may inadvertently encounter infected emails in their inbox, potentially compromising multiple accounts simultaneously. Security researchers have classified this vulnerability under CWE-79 which specifically addresses cross-site scripting flaws, and it aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments or links, though the execution occurs within the webmail application itself rather than through external browser exploits.
Organizations should immediately implement mitigations including updating to patched versions of Roundcube Webmail where available, implementing strict input validation policies, and deploying content security policies that prevent script execution in email contexts. Additional protective measures include configuring web application firewalls to detect and block suspicious javascript patterns in email content, implementing email filtering solutions that scan for malicious payloads, and conducting user awareness training to recognize potentially compromised emails. The vulnerability demonstrates the critical importance of validating all user-supplied input and properly escaping output in web applications, particularly those handling sensitive communication data. Security teams should also consider implementing monitoring solutions that can detect anomalous behavior patterns consistent with XSS exploitation attempts, as well as regular security assessments of webmail environments to identify similar vulnerabilities that may exist in other components or third-party integrations.