CVE-2025-53839 is a medium-severity cross-site scripting (XSS) vulnerability affecting versions of the DRACOON Branding Service prior to 2.10.0. DRACOON is a file sharing platform widely used for secure enterprise collaboration, and its Branding Service allows customers to customize the user interface with their own branding elements. The vulnerability arises from improper neutralization of input provided by administrative users during the web page generation process. Specifically, malicious HTML or script code can be injected into the onboarding workflow for newly onboarded users. This flaw is categorized under CWE-79, which involves improper sanitization of input leading to XSS attacks. The vulnerability requires high privileges (administrative user) to exploit, and user interaction is needed as the malicious payload is delivered through the onboarding process. The CVSS v3.1 score is 4.0 (medium), reflecting limited impact on confidentiality and integrity, no impact on availability, and the requirement for both privileges and user interaction. No known exploits are currently reported in the wild. The vendor has addressed this issue in version 2.10.0 of the DRACOON Branding Service, and the fix has been rolled out to the DRACOON service, with no further action required from customers.

For European organizations using DRACOON, this vulnerability could allow an attacker with administrative access to inject malicious scripts into the onboarding workflow, potentially leading to session hijacking, credential theft, or unauthorized actions performed by newly onboarded users. While the impact is limited by the need for administrative privileges and user interaction, the risk remains significant in environments where administrative accounts are shared, poorly managed, or compromised. Confidentiality and integrity of user sessions and data could be affected, particularly in sectors handling sensitive or regulated information such as finance, healthcare, and government. The vulnerability does not affect availability, but successful exploitation could facilitate further attacks or lateral movement within an organization’s network. Given DRACOON’s adoption in European enterprises for secure file sharing, exploitation could undermine trust in the platform and lead to compliance issues under regulations like GDPR if personal data is exposed.

Organizations should ensure that all instances of the DRACOON Branding Service are updated to version 2.10.0 or later, where the vulnerability is fixed. Since the vendor has rolled out the patch to the DRACOON service, customers using the cloud-hosted version may already be protected, but on-premises deployments must be verified and updated promptly. Additionally, organizations should enforce strict administrative account management policies, including the use of multi-factor authentication (MFA), least privilege principles, and regular auditing of administrative actions. Monitoring onboarding workflows for anomalous behavior or unexpected HTML/script content can help detect exploitation attempts. Web application firewalls (WAFs) configured to detect and block XSS payloads may provide an additional layer of defense. User training to recognize suspicious activities during onboarding can also reduce the risk of successful exploitation. Finally, organizations should review and tighten input validation and output encoding practices in any custom branding or interface customization to prevent similar vulnerabilities.