CVE-2024-25628

Executive Summary

CVE-2024-25628 is a critical authentication bypass vulnerability in Alf.io, an open-source event attendance management system. The flaw allows an attacker to access the admin area even after their user session has been invalidated or their account deleted. This effectively breaks the session management and access control mechanisms, enabling unauthorized administrative access. The vulnerability affects all versions prior to 2.0-M4-2402. The CVSS score is 7.6 (High), and while no public proof-of-concept (PoC) or exploit code is currently available, the risk is significant due to the potential for full administrative compromise of event management data.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
• Base Score: 7.6 (High)
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication is needed to exploit the flaw.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality (C): High (H) – Sensitive admin data can be accessed.
• Integrity (I): High (H) – Admin actions can be performed.
• Availability (A): None (N) – No direct impact on availability.

Threat Level: High. The lack of required privileges and low attack complexity make this a prime target for automated scanning and exploitation.

Deep Dive & Mechanics

The vulnerability stems from improper session invalidation within Alf.io's authentication framework. When a user is logged in as an administrator, the system creates a session token. If the admin account is subsequently deleted or the session is explicitly invalidated (e.g., via logout or admin action), the backend fails to properly revoke the associated session token. This allows the token to remain valid for subsequent requests, granting continued access to the admin area.

The root cause is likely a missing or flawed check in the session validation middleware. The system may rely on a cached or stale session state, or it may not verify the session against the current user database on every request. This is a classic example of CWE-287 (Improper Authentication), where the application does not properly verify that the user's session is still valid and authorized.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-2.0-M4-2402): The vulnerable code likely resides in the session validation filter or interceptor. A simplified example of the flawed logic:

// Vulnerable: Does not check if user still exists or session is revoked
public boolean isSessionValid(HttpSession session) {
    String userId = (String) session.getAttribute("userId");
    return userId != null; // Only checks if attribute exists
}

Patched Code (2.0-M4-2402): The patch introduces a database lookup to verify the user's existence and session status.

// Patched: Verifies user exists and session is not revoked
public boolean isSessionValid(HttpSession session) {
    String userId = (String) session.getAttribute("userId");
    if (userId == null) return false;
    User user = userRepository.findById(userId);
    return user != null && user.isActive() && !sessionRevoked(session.getId());
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

1. Setup: Deploy a vulnerable version of Alf.io (e.g., 2.0-M3) in a lab environment.
2. Obtain Admin Session: Log in as an admin user and capture the session cookie (e.g., JSESSIONID).
3. Invalidate Session: Have the admin account deleted or the session invalidated by another admin.
4. Reuse Session: Use the captured session cookie in subsequent requests to access admin endpoints (e.g., /admin/dashboard).
5. Verify Access: If the server returns admin-level data, the exploit is successful.

Example cURL command:

curl -X GET https://target-alfio.com/admin/dashboard \
  -H "Cookie: JSESSIONID=ABC123DEF456"

Blue Team (Defense & Detection)

1. Monitor Session Reuse: Log and alert on any use of session tokens that were previously invalidated.
2. Enforce Session Validation: Ensure the application validates sessions against the database on every request.
3. Implement Short Session Timeouts: Reduce the window of opportunity for token reuse.
4. Audit Logs: Review access logs for repeated use of the same session token after account deletion events.

Indicators of Compromise (IOCs)

• Session Token Reuse: The same JSESSIONID or similar token appearing in logs after the associated user account has been deleted.
• Unexpected Admin Access: Access to /admin/* endpoints from IP addresses or user agents not associated with known admin accounts.
• Log Anomalies: Multiple successful admin actions from a session that was previously invalidated.

Example Log Entry (Suspicious):

2024-03-15 10:00:00 - User "admin@example.com" deleted by "superadmin"
2024-03-15 10:05:00 - Session "ABC123DEF456" accessed /admin/dashboard (User: admin@example.com)

Detection Engineering

YARA Rule

rule CVE_2024_25628_Session_Reuse {
    meta:
        description = "Detects session reuse after account deletion in Alf.io logs"
        author = "Valters IT"
        date = "2024-03-15"
        reference = "CVE-2024-25628"
    strings:
        $s1 = "deleted by" ascii wide nocase
        $s2 = "accessed /admin" ascii wide nocase
        $s3 = "Session" ascii wide nocase
    condition:
        all of ($s*) and #s1 > 0 and #s2 > 0
}

Sigma Rule

title: Alf.io Admin Session Reuse After Deletion
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2024-25628 where an admin session is reused after account deletion.
author: Valters IT
date: 2024/03/15
logsource:
    category: application
    product: alfio
detection:
    selection:
        event: "deleted by"
    timeframe: 5m
    condition: selection | count() by src_ip > 1
falsepositives:
    - Legitimate admin re-login after deletion (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-25628 Alf.io Admin Session Reuse"; flow:to_server,established; content:"/admin/"; http_uri; content:"JSESSIONID"; http_cookie; pcre:"/JSESSIONID=[A-Z0-9]{32}/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade to Alf.io version 2.0-M4-2402 or later.
2. Workaround: No known workarounds exist. If immediate upgrade is not possible, restrict network access to the admin interface (e.g., via VPN or IP whitelisting).
3. Long-term: Implement additional session validation checks, such as verifying user existence and session revocation status on every request.
4. Monitoring: Enable detailed logging for all admin actions and session events. Set up alerts for anomalous session reuse patterns.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert