CVE-2026-48164 in Online
Summary
by MITRE • 10/30/2026
Collabora Online is a collaborative online office suite based on LibreOffice technology. Prior to 24.04.18 and 25.04.11, the `host_session_id` query/form parameter is substituted into the `cool.html` editor page without HTML encoding, unlike parameters passed through the existing variable-encoding mechanism. An attacker who induces a victim to load a crafted URL can inject HTML and, in the absence of an effective `Content Security Policy`, execute scripts in the Collabora Online iframe's origin, exposing the session authentication token and page contents. A reverse proxy that preserves the `Content Security Policy` header sent by `coolwsd` mitigates the script-execution scenario. This issue is fixed in versions 24.04.18 and 25.04.11.
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Analysis
by VulDB Data Team • 10/30/2026
Collabora Online, a widely deployed collaborative office suite built upon LibreOffice technology, was found to contain a significant input validation flaw affecting versions prior to 24.04.18 and 25.04.11. The vulnerability centers on the improper handling of the host_session_id query or form parameter within the cool.html editor page interface. Unlike other parameters that are processed through an existing variable-encoding mechanism designed to sanitize input, this specific identifier is substituted directly into the HTML structure without any form of encoding or escaping. This inconsistency in data processing creates a direct pathway for injection attacks, as the application fails to distinguish between trusted structural content and untrusted user-supplied data when rendering the editor interface.
The technical nature of this flaw constitutes an Unsanitized Input vulnerability that leads directly to Cross-Site Scripting, specifically categorized under CWE-79 in industry standards. Because the host_session_id parameter is injected into the DOM without sanitization, an attacker can craft a malicious URL containing embedded HTML and JavaScript payloads. When a victim user loads this crafted link within their browser while authenticated with Collabora Online, the browser interprets the injected code as part of the page's legitimate script context. This allows for the execution of arbitrary scripts within the origin of the Collabora Online iframe, bypassing standard isolation boundaries if security policies are not strictly enforced.
The operational impact of this vulnerability is severe due to its potential for session hijacking and data exfiltration. Successful exploitation enables an attacker to access sensitive information stored in the browser's local storage or cookies associated with the Collabora Online domain. Specifically, the script execution can expose the session authentication token, which grants the attacker full control over the victim's active editing sessions. Furthermore, because the scripts run within the iframe's origin, they have direct read and write access to page contents, allowing for the theft of document data or the modification of documents without authorization. This effectively compromises both confidentiality and integrity of the collaborative workspace.
Mitigation strategies focus on enforcing strict security headers and applying immediate software updates. The most effective defense against script execution in this scenario is a robust Content Security Policy that restricts inline script execution and limits sources from which scripts can be loaded. A reverse proxy positioned in front of the Collabora Online server must preserve and enforce these CSP headers sent by coolwsd to prevent the injection of malicious code even if input validation fails. Additionally, organizations should prioritize upgrading to version 24.04.18 or 25.04.11 where this encoding inconsistency has been resolved. From a threat intelligence perspective, this vulnerability aligns with ATT&CK techniques related to Client-side Scripting and Session Hijacking, highlighting the need for continuous monitoring of web application parameters that interact directly with DOM elements without adequate sanitization protocols.