CVE-2026-114720 in Roundcube
Summary
by MITRE • 10/22/2026
Roundcube Webmail before 1.6.20 and 1.7.x before 1.7.5 is affected by an IMAP command injection vulnerability. A remote authenticated attacker can exploit this via CRLF sequences injected into the _flag parameter of the mail/mark action to execute arbitrary IMAP commands. Upstream fixed this in the commit “Fix IMAP command injection via CRLF in `_flag` parameter of mail/mark action”, which rejects flags containing control, whitespace and IMAP-special characters.
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Analysis
by VulDB Data Team • 10/22/2026
Roundcube Webmail versions prior to 1.6.20 and 1.7.x prior to 1.7.5 contain a critical server-side request forgery vulnerability that manifests as an IMAP command injection flaw. This security issue arises from insufficient input validation within the mail/mark action, specifically concerning the _flag parameter used for marking messages with flags such as read or deleted. The underlying technical defect allows remote authenticated attackers to inject Carriage Return and Line Feed sequences into this parameter. By carefully crafting these CRLF characters, an attacker can terminate the intended IMAP command line and append a new, arbitrary IMAP command to the request stream sent from Roundcube to the backend mail server. This technique effectively bypasses standard input sanitization mechanisms that might otherwise filter out obvious malicious payloads but fail to account for control character injection via whitespace manipulation.
The operational impact of this vulnerability is severe because it grants an authenticated user the ability to execute arbitrary commands on the underlying IMAP infrastructure. Since Roundcube acts as a proxy between the web client and the mail server, successfully injecting commands allows the attacker to perform actions that may extend beyond simple message flagging. Depending on the specific IMAP implementation and configuration of the target mail server, this could lead to unauthorized access to other folders, deletion or modification of arbitrary messages, retrieval of sensitive email content, or potentially further exploitation if the backend service is vulnerable to additional command injection vectors. The attack requires authentication, meaning an attacker must first compromise valid user credentials through phishing, credential stuffing, or other means before leveraging this vulnerability for lateral movement within the mail system environment.
From a classification perspective, this flaw aligns with CWE-94 Improper Control of Generation of Code Command Injection and falls under MITRE ATT&CK technique T1059 Command and Scripting Interpreter where the IMAP protocol is treated as an interpreter executing injected commands. The vulnerability highlights the risks associated with passing unsanitized user input directly into backend service protocols without rigorous validation against a strict allowlist of expected characters. The presence of control characters like carriage returns and line feeds in parameters intended for simple string values creates a vector for breaking out of the current command context, which is a classic pattern in injection-based attacks across various networked applications.
The upstream developers addressed this issue by implementing stricter input validation logic that explicitly rejects flags containing control characters, whitespace, or IMAP-special characters. This mitigation strategy ensures that only alphanumeric and safe punctuation marks are accepted for flag values, thereby preventing the insertion of CRLF sequences necessary to split command lines. Organizations running affected versions should prioritize upgrading to Roundcube 1.6.20 or 1.7.5 immediately to close this attack vector. In addition to patching, administrators should enforce strong authentication policies and consider implementing web application firewalls that can detect anomalous IMAP traffic patterns indicative of injection attempts as a defense-in-depth measure while updates are being deployed across the infrastructure.