CVE-2025-59683

Executive Summary

CVE-2025-59683 is a critical Improper Access Control vulnerability in Pexip Infinity versions 15.0 through 38.0 (before 38.1). The flaw resides in the Secure Scheduler for Exchange service when configured to use Office 365 Legacy Exchange Tokens. A remote, unauthenticated attacker can exploit this to read potentially sensitive data and cause excessive resource consumption, leading to a denial of service (DoS). The CVSS score is 8.2 (High), driven by network attack vector, low complexity, and no privileges required. No public proof-of-concept or exploit code is currently available, but the vulnerability is considered high risk due to the potential for data leakage and service disruption.

CVSS Breakdown & Threat Level

• CVSS Score: 8.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
• Attack Vector (AV): Network – Exploitable remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): None – No user action required.
• Scope (S): Unchanged – Exploit does not affect other components.
• Confidentiality (C): Low – Limited sensitive data exposure.
• Integrity (I): None – No data modification.
• Availability (A): High – Significant resource exhaustion leading to DoS.

Threat Level: High. The combination of remote exploitation, low complexity, and potential for both data leakage and denial of service makes this a serious threat for organizations using Pexip Infinity with Office 365 Legacy Exchange Tokens.

Deep Dive & Mechanics

The vulnerability exists in the Secure Scheduler for Exchange service, which is responsible for integrating Pexip Infinity with Microsoft Exchange/Office 365 for scheduling video conferences. When configured to use Office 365 Legacy Exchange Tokens (an older authentication mechanism), the service fails to properly validate access controls on incoming requests.

Root Cause: Improper Access Control (CWE-284). The service does not enforce adequate authorization checks before processing requests. An attacker can craft malicious requests that bypass authentication or authorization, allowing them to:

• Access sensitive data (e.g., meeting details, user information, calendar data) that should be restricted.
• Trigger resource-intensive operations (e.g., excessive database queries, token validation loops) that consume CPU, memory, or network bandwidth, leading to a denial of service.

Attack Vector: The attacker sends specially crafted HTTP/HTTPS requests to the Secure Scheduler for Exchange endpoint. Since the service is exposed on the network (typically on standard ports like 443), no prior access is required.

Impact:

• Confidentiality: Exposure of sensitive scheduling data, potentially including meeting topics, participant lists, and timestamps.
• Availability: Service disruption for legitimate users due to resource exhaustion.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-38.1): The vulnerable code likely lacks proper authorization checks in the request handler for the Secure Scheduler for Exchange service. For example, a function that processes incoming requests might not verify the user's identity or permissions before executing sensitive operations.

# Vulnerable pseudocode
def handle_scheduler_request(request):
    # No access control check
    data = fetch_sensitive_data(request.parameters)
    return data

Patched Code (38.1+): The patched version introduces proper access control validation, likely by verifying tokens or session credentials before processing.

# Patched pseudocode
def handle_scheduler_request(request):
    if not validate_access_token(request.token):
        return "Unauthorized", 403
    data = fetch_sensitive_data(request.parameters)
    return data

The exact patch details are not publicly available, but the fix involves enforcing authentication and authorization checks on all endpoints of the Secure Scheduler for Exchange service.

Exploitation & Lab Setup

Red Team (Offensive):

Since no public exploit code exists, a red team would need to reverse-engineer the service or perform black-box testing. The following steps outline a potential exploitation approach:

1. Reconnaissance: Identify Pexip Infinity instances using Shodan dorks (e.g., "Pexip Infinity"). Confirm the version is between 15.0 and 38.0.
2. Endpoint Discovery: Scan for the Secure Scheduler for Exchange service endpoints (e.g., /scheduler, /exchange).
3. Token Manipulation: Attempt to send requests without a valid token or with a forged Legacy Exchange Token.
4. Resource Exhaustion: Send a high volume of requests to trigger DoS.

Lab Setup:

• Target: Pexip Infinity 38.0 (vulnerable) running in a VM.
• Attacker: Kali Linux with tools like curl, Burp Suite, and custom Python scripts.
• Network: Both machines on the same subnet.

Example Request (Hypothetical):

curl -X GET "https://target.pexip.local/scheduler/meetings" -H "Authorization: Bearer forged_token"

Blue Team (Defensive):

• Detection: Monitor for unusual traffic patterns to the Secure Scheduler for Exchange endpoints, especially from unknown IPs.
• Mitigation: Immediately upgrade to version 38.1 or later. If upgrade is not possible, restrict network access to the service using firewall rules or VPNs.
• Honeypot: Deploy a decoy Pexip instance to capture attacker behavior.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unusual HTTP requests to /scheduler/ or /exchange/ endpoints.
  • High volume of requests from a single IP address.
  • Requests with invalid or missing authentication tokens.
• System IOCs:
  • High CPU or memory usage on the Pexip server.
  • Log entries showing failed authentication attempts or unauthorized access.
  • Unexplained service crashes or restarts.

Detection Engineering

YARA Rule:

rule CVE_2025_59683_Pexip_Infinity_Access_Control {
    meta:
        description = "Detects exploitation attempts for CVE-2025-59683"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-59683"
    strings:
        $scheduler_path = "/scheduler/"
        $exchange_path = "/exchange/"
        $legacy_token = "LegacyExchangeToken"
    condition:
        any of ($scheduler_path, $exchange_path) and $legacy_token
}

Sigma Rule:

title: CVE-2025-59683 - Pexip Infinity Improper Access Control
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects exploitation attempts for CVE-2025-59683
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: pexip
detection:
    selection:
        cs-uri-stem:
            - '/scheduler/*'
            - '/exchange/*'
        cs-method: 'GET'
        cs-user-agent: '*'
    condition: selection
falsepositives:
    - Legitimate administrative access
level: high

Suricata Rule:

alert http any any -> any any (msg:"CVE-2025-59683 - Pexip Infinity Improper Access Control"; flow:to_server; content:"/scheduler/"; http_uri; content:"/exchange/"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: Update Pexip Infinity to version 38.1 or later. This is the only confirmed fix.
2. Workaround: If upgrade is not possible, disable the use of Office 365 Legacy Exchange Tokens and switch to modern authentication (OAuth 2.0).
3. Network Segmentation: Restrict access to the Secure Scheduler for Exchange service to trusted IP ranges only.

Long-Term Measures:

• Implement regular vulnerability scanning for Pexip Infinity.
• Monitor vendor advisories for future patches.
• Enforce least-privilege access controls on all services.

Valters IT Signature: This report was generated by Valters IT Cyber Threat Intelligence Division. For questions, contact threatintel@valtersit.com.