CVE-2024-31213

Executive Summary

CVE-2024-31213 identifies an open redirect vulnerability in InstantCMS version 2.16.2. The flaw is triggered when a user modifies their own profile, allowing an attacker to craft a malicious redirect URL. This can be leveraged for phishing attacks, where a victim is redirected to an attacker-controlled site that mimics the CMS login or profile update page, potentially capturing credentials. The CVSS score is 3.5 (Low), but the social engineering aspect elevates the risk in targeted attacks. No patch is currently available, and no public exploit code has been released.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
• Base Score: 3.5 (Low)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: Low
• Availability Impact: None

The low score reflects the need for user interaction and the limited direct impact. However, in a phishing campaign, the integrity impact can be leveraged to steal credentials, leading to higher severity in practice.

Deep Dive & Mechanics

The vulnerability resides in the profile update functionality of InstantCMS. After a user submits changes to their profile, the application performs a redirect. The redirect URL is not properly validated, allowing an attacker to inject a malicious external URL. The flow is as follows:

1. User logs into InstantCMS.
2. User navigates to profile edit page.
3. User submits profile changes.
4. The application processes the request and redirects the user to a URL that can be manipulated via parameters or referrer headers.
5. An attacker crafts a link that includes a malicious redirect target (e.g., https://evil.com/phish).
6. Victim clicks the link, completes the profile update, and is redirected to the attacker's site.
7. The attacker's site displays a fake login or password prompt, capturing credentials.

The lack of input sanitization on the redirect parameter is the root cause.

Vulnerable vs. Patched Code

Vulnerable Code (InstantCMS 2.16.2):

// In profile controller
$redirect = $_GET['redirect'] ?? '/profile';
header('Location: ' . $redirect);
exit;

Patched Code (Hypothetical fix):

// Validate redirect URL
$redirect = $_GET['redirect'] ?? '/profile';
$allowed_hosts = ['example.com', 'www.example.com'];
$parsed_url = parse_url($redirect);
if (in_array($parsed_url['host'], $allowed_hosts) || $parsed_url['host'] === null) {
    header('Location: ' . $redirect);
    exit;
} else {
    header('Location: /profile');
    exit;
}

The fix adds a whitelist of allowed hosts and validates the redirect URL against it.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install InstantCMS 2.16.2 on a local server (e.g., XAMPP or Docker).
2. Create a user account and log in.
3. Craft a malicious link: http://target-cms.com/profile/edit?redirect=http://evil.com/phish
4. Send the link to the victim via email or social engineering.
5. Victim clicks, updates profile, and is redirected to evil.com/phish.
6. On evil.com, host a fake login page that captures credentials.

Proof of Concept (No public exploit available):

# Simple curl test to verify redirect
curl -v "http://target-cms.com/profile/edit?redirect=http://evil.com"

Blue Team

Detection:

• Monitor for unusual redirect parameters in profile update requests.
• Look for outbound connections to suspicious domains after profile updates.
• Use web application firewall (WAF) rules to block open redirect patterns.

Hunting:

• Search logs for redirect= parameter in profile edit URLs.
• Correlate with subsequent connections to unknown external hosts.

Indicators of Compromise (IOCs)

• URL Pattern: /profile/edit?redirect=http:// or https:// followed by an external domain.
• Network: Outbound HTTP requests to domains not whitelisted for redirects.
• Logs: GET /profile/edit?redirect=http://evil.com entries in web server logs.
• Phishing Page: Fake login forms hosted on attacker-controlled domains.

Detection Engineering

YARA Rule

rule CVE_2024_31213_Open_Redirect {
    meta:
        description = "Detects open redirect attempts in InstantCMS profile edit"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-31213"
    strings:
        $redirect_param = "redirect="
        $profile_edit = "/profile/edit"
        $external_url = /(http|https):\/\/[^\/]+\.[a-z]{2,}/
    condition:
        $redirect_param and $profile_edit and $external_url
}

Sigma Rule

title: InstantCMS Open Redirect via Profile Edit
id: 8f2a1b3c-4d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects open redirect attempts in InstantCMS profile edit functionality
author: Valters IT
date: 2024/01/01
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: GET
        cs-uri-stem: '/profile/edit'
        cs-uri-query|contains: 'redirect='
    condition: selection
falsepositives:
    - Legitimate redirects to same domain
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-31213 InstantCMS Open Redirect"; flow:to_server; content:"/profile/edit"; http_uri; content:"redirect="; http_uri; pcre:"/redirect=(http|https):\/\//Ri"; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the profile edit functionality if not essential.
2. Implement a web application firewall (WAF) rule to block external redirects.
3. Monitor logs for suspicious redirect patterns.

Long-term Fix:

• Apply input validation on the redirect parameter, allowing only relative paths or whitelisted domains.
• Upgrade to a patched version once available (currently none).
• Consider using a security plugin or custom code to sanitize redirects.

Workaround:

• Modify the source code to hardcode the redirect to a safe URL (e.g., /profile).

Valters IT
Securing Digital Frontiers