Overview
CVE-2025-59788 is a cross-site scripting (XSS) vulnerability identified in the files_pdfviewer example directory of Nextcloud. This vulnerability affects versions prior to 22.2.10.33, 23.0.12.29, 24.0.12.28, 25.0.13.23, 26.0.13.20, 27.1.11.20, 28.0.14.11, 29.0.16.8, 30.0.17, 31.0.10, and 32.0.1. An attacker can exploit this vulnerability to execute arbitrary JavaScript code within a user’s browser session by crafting a malicious PDF file and targeting the viewer.html file. This issue stems from exposing executable example code on a same-origin basis. It is related to CVE-2024-4367, highlighting the importance of addressing insecure example code practices.
Technical Details
The vulnerability resides within the files_pdfviewer application, specifically in the example code provided with the application. The viewer.html file, intended for demonstration purposes, is susceptible to XSS attacks. By crafting a PDF file containing malicious JavaScript and persuading a user to open it within the viewer.html, an attacker can inject arbitrary scripts into the user’s browser. These scripts execute within the context of the Nextcloud domain, potentially allowing the attacker to steal cookies, modify the page content, or perform actions on behalf of the user.
The root cause is due to the presence of executable example code in a publicly accessible directory on a same-origin basis. This means that scripts loaded from the same domain as the Nextcloud instance can access the same cookies and local storage as the main application, leading to a significant security risk when XSS vulnerabilities are present.
CVSS Analysis
- CVE ID: CVE-2025-59788
- Severity: MEDIUM
- CVSS Score: 6.4
A CVSS score of 6.4 indicates a medium severity vulnerability. While the attack requires user interaction (opening a crafted PDF), the potential impact on confidentiality, integrity, and availability is significant. An attacker could potentially compromise user accounts or sensitive data.
Possible Impact
Successful exploitation of this vulnerability can lead to the following consequences:
- Account Compromise: An attacker could steal user session cookies and gain unauthorized access to Nextcloud accounts.
- Data Theft: Malicious scripts could be used to extract sensitive data stored within Nextcloud.
- Defacement: The attacker could modify the appearance of the Nextcloud interface, leading to phishing attacks or misinformation.
- Malware Distribution: The attacker could use the compromised Nextcloud instance to distribute malware to other users.
Mitigation or Patch Steps
To mitigate this vulnerability, it is strongly recommended to update your Nextcloud instance to one of the following versions (or later):
- 22.2.10.33
- 23.0.12.29
- 24.0.12.28
- 25.0.13.23
- 26.0.13.20
- 27.1.11.20
- 28.0.14.11
- 29.0.16.8
- 30.0.17
- 31.0.10
- 32.0.1
You can update your Nextcloud instance through the built-in updater or by following the official Nextcloud upgrade instructions. Regular security updates are crucial to protect your data and maintain the integrity of your Nextcloud installation.
