CVE-2026-65053 in Imp
Summary
by MITRE • 08/24/2026
Horde IMP's AppleDouble MIME viewer writes an attacker-controlled attachment name into an HTML status block without escaping it. In lib/Mime/Viewer/Appledouble.php, _IMPrender() obtains the name of the data part with IMP_Contents::getPartName(), which returns the MIME part's own name parameter as supplied by the message, and passes it through sprintf into the text of an IMP_Mime_Status object. IMP_Mime_Status::__toString() concatenates each text entry directly into the surrounding table markup, so the value reaches the rendered page verbatim. A message crafted as multipart/appledouble whose data part carries markup in its name parameter therefore executes script in the context of any user who views it, and the payload persists in the mailbox. Exploitation requires no account on the target system, only the ability to send mail to a user. Version 7.2.0 escapes the value with htmlspecialchars(). The researcher additionally chains this flaw with the arbitrary file read of CVE-2026-58451, and reports that script running in an administrator's session can reach an application code-execution path.
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Analysis
by VulDB Data Team • 08/24/2026
The vulnerability identified as a cross-site scripting (XSS) flaw within Horde IMP represents a classic case of insufficient input validation and output encoding in web applications handling user-supplied data. Specifically, the defect resides in the AppleDouble MIME viewer component located at lib/Mime/Viewer/Appledouble.php. The core technical failure occurs during the rendering process where the function _IMPrender() retrieves the filename associated with a specific MIME part by invoking IMP_Contents::getPartName(). This method returns the name parameter directly from the incoming message without performing any sanitization or encoding checks. Subsequently, this untrusted value is passed into an sprintf call to construct text content for an IMP_Mime_Status object. The critical failure point arises when the IMP_Mime_Status::__toString() method concatenates these text entries directly into HTML table markup. Because no escaping mechanism such as htmlspecialchars was applied before insertion into the DOM structure, any special characters or script tags embedded within the attachment name are rendered verbatim by the browser. This architectural oversight allows an attacker to inject malicious JavaScript payloads simply by crafting a multipart/appledouble email where the data part's name parameter contains executable code.
From an operational perspective, this vulnerability facilitates persistent cross-site scripting attacks that do not require authentication from the attacker’s side. The primary requirement for exploitation is merely the ability to send an email message to a target user within the Horde IMP system. Once received, the malicious payload remains stored in the mailbox and executes whenever any authorized user views the message through their web browser session. This persistence distinguishes it from reflected XSS attacks, as the script resides on the server-side storage before being served to victims. The impact is severe because it allows attackers to hijack user sessions, steal sensitive cookies or authentication tokens, perform actions on behalf of the victim, and potentially exfiltrate confidential data displayed within the application interface. Since Horde IMP is often used for enterprise email management, compromising a single account can lead to broader organizational security breaches if privilege escalation techniques are employed later in the attack chain.
The vulnerability aligns with CWE-79, which classifies improper neutralization of input during web page generation as Cross-site Scripting (XSS). In terms of offensive security frameworks, this flaw maps directly to MITRE ATT&CK technique T1059.007, specifically JavaScript execution within a browser environment. The attack vector is classified under Remote Code Execution via Web Application Components, leveraging the trust relationship between the user and the web application interface. The persistence mechanism ensures that the threat remains active across multiple viewing sessions until the malicious email is deleted or the vulnerability is patched. This type of flaw highlights the critical importance of implementing strict output encoding for all dynamic content derived from external sources, particularly when that content is embedded directly into HTML structures without intermediate sanitization layers.
Mitigation strategies focus on enforcing secure coding practices regarding data handling and display. The most effective remediation involves applying context-sensitive output encoding to any user-supplied data before it is inserted into the DOM. In this specific instance, version 7.2.0 of Horde IMP addresses the issue by integrating htmlspecialchars() calls around the attachment name value prior to its inclusion in the HTML markup. This function converts special characters such as ampersands, less-than signs, greater-than signs, and quotes into their corresponding HTML entities, thereby preventing them from being interpreted as executable code or structural elements by the browser. Organizations running older versions must apply this patch immediately. Additionally, implementing Content Security Policy headers can provide a defense-in-depth layer by restricting the sources from which scripts are allowed to execute, reducing the impact even if an injection succeeds. Regular security audits and static analysis tools should be employed to detect similar patterns of unescaped variable interpolation in other parts of the application codebase.
Furthermore, this vulnerability is not isolated but can be chained with other flaws to escalate privileges significantly. Researchers have demonstrated that when combined with CVE-2026-58451, an arbitrary file read vulnerability within the same system, the impact expands from simple script execution to potential full application code execution. An attacker who successfully exploits the XSS flaw in a session belonging to an administrator can leverage their elevated privileges to access sensitive files via the adjacent file read weakness. This combination allows for sophisticated attack chains where initial low-privilege access is leveraged through social engineering or external email delivery, followed by privilege escalation and deeper system compromise. Such chaining scenarios underscore the necessity of holistic vulnerability management rather than addressing individual flaws in isolation. Security teams must evaluate how multiple weaknesses interact within an application architecture to understand the true risk profile and prioritize remediation efforts accordingly.