CVE-2026-124491 in SunEditor
Summary
by MITRE • 11/08/2026
SunEditor before 3.4.0 contains a stored cross-site scripting vulnerability in the FileUpload plugin create() method that assigns server-returned file names to innerHTML without escaping. Attackers can upload files with HTML-laden names that bypass html.clean() and execute JavaScript in victims' browsers when content or gallery items load, enabling session theft.
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Analysis
by VulDB Data Team • 11/08/2026
The vulnerability identified in SunEditor versions prior to 3.4.0 represents a critical security flaw within the FileUpload plugin's create method. This issue stems from an improper neutralization of special elements during input validation and output encoding, specifically classified under CWE-79: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). The core technical failure occurs when the application accepts file uploads and subsequently assigns server-returned filenames directly to the innerHTML property of DOM elements. This assignment is performed without adequate escaping or sanitization, allowing maliciously crafted input to be interpreted as executable code rather than plain text data by the browser's rendering engine.
The attack vector relies on an attacker uploading a file with a name containing embedded HTML and JavaScript payloads. Although SunEditor includes a cleaning function known as html.clean(), this mechanism fails to adequately filter or escape specific script-injecting patterns within filenames during the upload process. Consequently, when the editor renders content that references these uploaded files, such as in gallery views or inline text insertion, the malicious filename is injected into the DOM structure. Because the injection occurs via innerHTML assignment rather than user input fields on a form page, this constitutes a stored cross-site scripting vulnerability where the payload persists on the server and executes automatically for any victim who loads the affected content.
The operational impact of this flaw is severe, primarily facilitating session hijacking and unauthorized access to user accounts. By executing arbitrary JavaScript in the context of the vulnerable application, an attacker can steal sensitive information such as authentication cookies, session tokens, or other credentials stored in browser storage. This capability allows for complete compromise of the victim's account privileges without requiring further interaction beyond viewing the compromised content. The persistence of the payload means that multiple users may be affected each time they access pages containing the tainted file references, amplifying the scope of potential damage significantly compared to reflected XSS attacks which require direct user engagement with a crafted link.
From an industry standard perspective, this vulnerability aligns closely with MITRE ATT&CK technique T1059: Command and Scripting Interpreter, specifically through browser-based scripting languages like JavaScript. The exploitation path demonstrates how web application frameworks can inadvertently become vectors for client-side code execution if input handling is not rigorously secured against injection attacks. Developers must recognize that even data retrieved from server responses requires strict validation before being rendered in the DOM, regardless of whether it originates from user uploads or other backend processes.
To mitigate this vulnerability, immediate updates to SunEditor version 3.4.0 or later are required as these versions address the flawed input handling logic within the FileUpload plugin. In environments where upgrading is not immediately feasible, a temporary mitigation involves implementing strict server-side validation of file names before they are stored in the database or filesystem. This includes rejecting filenames that contain characters commonly used in HTML tags and script injections, such as angle brackets, quotes, and ampersands. Additionally, applying Content Security Policy headers can help restrict the execution of inline scripts, thereby reducing the impact if an injection attempt succeeds. Long-term remediation should involve adopting a whitelist approach for allowed filename characters and ensuring that all dynamic content insertion uses textContent instead of innerHTML where possible to prevent DOM-based script execution entirely.