CVE-2025-29459

Executive Summary

CVE-2025-29459 is a disputed information disclosure vulnerability in MyBB 1.8.38. The issue involves the Mail function, which may allow a remote attacker with administrative privileges to obtain sensitive information. The vendor disputes this, citing that the actions are within the allowed scope of Board administrators and that SSRF mitigations are in place. The CVSS score is 0.0, indicating no official severity rating, but the potential for information leakage remains. No public proof-of-concept or exploit code is available at this time.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a standalone PHP application (MyBB) vulnerability.

CVSS Breakdown & Threat Level

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

Threat Level: Low. Exploitation requires administrative credentials, and the impact is limited to information disclosure. The vendor's dispute and SSRF mitigations further reduce the practical risk.

Deep Dive & Mechanics

The vulnerability resides in MyBB's Mail function, which is used to send emails from the administration panel. The issue likely involves improper sanitization of email headers or parameters, allowing an attacker to inject malicious content that could be reflected in error messages or logs, leading to information disclosure.

Root Cause: The Mail function may not properly validate or sanitize user-supplied input (e.g., email addresses, headers) before processing. This could allow an attacker to craft a request that causes the system to leak internal configuration details, file paths, or other sensitive data in error responses.

Attack Vector: An authenticated administrator with access to the Mail settings can craft a malicious email request. The attacker could manipulate parameters such as to, from, subject, or headers to trigger an error that reveals sensitive information.

Dispute: The vendor argues that Board administrators are trusted users and that SSRF mitigations prevent external exploitation. However, the potential for internal information leakage remains a concern, especially in multi-tenant or shared hosting environments.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is presumed to be in the Mail function of MyBB 1.8.38. The following is a hypothetical comparison based on common information disclosure vulnerabilities.

Vulnerable Code (MyBB 1.8.38):

// Vulnerable: Directly outputs error message with sensitive data
function send_mail($to, $subject, $message, $headers) {
    $result = mail($to, $subject, $message, $headers);
    if (!$result) {
        echo "Mail failed: " . error_get_last()['message'];
    }
}

Patched Code (Hypothetical):

// Patched: Sanitizes error output and logs internally
function send_mail($to, $subject, $message, $headers) {
    $result = mail($to, $subject, $message, $headers);
    if (!$result) {
        error_log("Mail failed: " . error_get_last()['message']);
        echo "Mail failed. Please check logs.";
    }
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Administrative access to MyBB 1.8.38
• Access to the Mail settings page

Exploitation Steps:

1. Log in as an administrator.
2. Navigate to the Mail settings (e.g., admin/index.php?module=config-mail).
3. Craft a malicious email request with specially crafted headers or parameters.
4. Observe the error response for sensitive information (e.g., file paths, database credentials).

Example Payload:

# Using curl to send a crafted request
curl -X POST "http://target/admin/index.php?module=config-mail" \
  -d "to=test@test.com&subject=Test&message=Test&headers=From: <?php phpinfo(); ?>"

Note: No public exploit code is available. The above is a conceptual example.

Blue Team

Detection:

• Monitor for unusual email sending activity from the admin panel.
• Look for error messages containing sensitive data in logs.
• Use the detection rules provided below.

Mitigation:

• Restrict administrative access to trusted users only.
• Implement strict input validation and output sanitization.
• Disable the Mail function if not required.

Indicators of Compromise (IOCs)

• Log Entries: Error messages containing file paths, database credentials, or other sensitive data.
• Network Traffic: Unusual outbound SMTP traffic from the MyBB server.
• File Changes: Modifications to MyBB configuration files (e.g., inc/config.php).

Detection Engineering

YARA Rule

rule CVE_2025_29459_MyBB_Mail_Disclosure {
    meta:
        description = "Detects attempts to exploit CVE-2025-29459 in MyBB 1.8.38"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-29459"
    strings:
        $s1 = "Mail failed" nocase
        $s2 = "error_get_last" nocase
        $s3 = "send_mail" nocase
    condition:
        any of ($s1, $s2, $s3)
}

Sigma Rule

title: CVE-2025-29459 MyBB Mail Information Disclosure
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2025-29459 in MyBB 1.8.38
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: mybb
detection:
    selection:
        EventID: 1
        Image|endswith: '/php'
        CommandLine|contains: 'send_mail'
    condition: selection
falsepositives:
    - Legitimate administrative email sending
level: low

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-29459 MyBB Mail Information Disclosure"; flow:to_server,established; content:"POST"; http_method; content:"/admin/index.php"; http_uri; content:"module=config-mail"; http_uri; content:"Mail failed"; http_server_body; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Restrict administrative access to trusted users only.
   • Monitor logs for suspicious email sending activity.
   • Disable the Mail function if not required.

2. Long-term Fix:

   • Apply any official patch from MyBB when available.
   • Implement strict input validation and output sanitization in the Mail function.
   • Use a Web Application Firewall (WAF) to filter malicious requests.

3. Workarounds:

   • Use a third-party SMTP service instead of the built-in Mail function.
   • Implement custom error handling to prevent information leakage.

Valters IT
Securing Digital Frontiers