CVE-2023-35075 is a vulnerability identified in the Mattermost web application, specifically related to improper neutralization of special elements in output used by a downstream component, classified under CWE-74 (Improper Neutralization of Special Elements in Output). The issue arises when the Mattermost webapp sets the channel name during autocomplete functionality. Instead of using safe properties such as innerText or textContent to assign the channel name, the application directly inserts the channel name as HTML. This allows an attacker to create a channel name containing valid HTML elements, which then get injected into the victim's page DOM. Although this injection does not lead to cross-site scripting (XSS) because script execution is not possible, it still represents an injection flaw that could potentially be leveraged for UI manipulation or phishing attempts within the Mattermost interface. The vulnerability has a CVSS 3.1 base score of 3.1, indicating low severity. It requires network access (AV:N), has high attack complexity (AC:H), requires low privileges (PR:L), and no user interaction (UI:N). The impact is limited to integrity (I:L) with no confidentiality or availability impact. No known exploits are currently reported in the wild, and no patches have been linked yet. The affected versions are not explicitly detailed but presumably include recent Mattermost releases prior to the fix. The core technical issue is the failure to sanitize or properly encode channel names before rendering them in the DOM, leading to injection of HTML elements that could alter the user interface or mislead users but not execute malicious scripts.

For European organizations using Mattermost as a collaboration and communication platform, this vulnerability could lead to minor integrity issues within the user interface. An attacker with the ability to create channels (which may require some level of privilege) could inject HTML elements that alter the appearance or behavior of the Mattermost client for other users. Although no direct code execution or data theft is possible, this could be exploited for social engineering or phishing attacks within the platform, potentially tricking users into revealing sensitive information or performing unintended actions. The low severity and lack of known exploits reduce the immediate risk, but organizations with high reliance on Mattermost for internal communications should consider the reputational and operational risks of UI manipulation. The impact is more pronounced in environments where channel creation is less restricted or where users may be less security-aware. Since Mattermost is often used in enterprise and government sectors, any manipulation of the interface could undermine trust in the platform and complicate incident response.

To mitigate this vulnerability, European organizations should: 1) Apply any official patches or updates from Mattermost as soon as they become available to ensure the issue is resolved at the source. 2) Implement strict access controls on who can create or rename channels within Mattermost to limit the ability of attackers to inject malicious HTML. 3) Monitor channel names for suspicious or unusual HTML content and enforce validation or sanitization policies at the application or proxy level if possible. 4) Educate users about the potential for UI manipulation and encourage vigilance against unexpected interface changes or phishing attempts within Mattermost. 5) Consider deploying Content Security Policy (CSP) headers to restrict the execution of inline scripts or loading of untrusted content, even though this vulnerability does not enable script execution directly. 6) Regularly audit Mattermost configurations and logs to detect any attempts to exploit this injection flaw. These steps go beyond generic advice by focusing on access control, monitoring, and user awareness tailored to the specific injection vector in Mattermost channel names.