CVE-2026-45117
Received Received - Intake

PHP Code Injection in MyBB Installer Module

Publication date: 2026-08-18

Last updated on: 2026-08-18

Assigner: GitHub, Inc.

Description
MyBB is free and open source forum software. From 1.8.13 until 1.8.40, the installer module does not properly escape user-supplied database configuration values written to the configuration file, resulting in PHP code injection and remote code execution when the installer is available. install/index.php processes the values with addcslashes(), but the $characters argument added in MyBB 1.8.13 does not include the backslash character, allowing crafted input to escape the generated PHP string. The uniquely identifying implementation details include introduced in MyBB 1.8.13. This issue is fixed in version 1.8.40.

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Meta Information

Published
2026-08-18
Last Modified
2026-08-18
Generated
2026-09-07
AI Q&A
2026-08-18
EPSS Evaluated
2026-09-06
NVD
CVE-2026-45117
EUVD
EUVD-2026-61020

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mybb mybb From 1.8.13 (inc) to 1.8.40 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-94 The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

Attack-Flow Graph

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Executive Summary

This vulnerability is a Remote Code Execution (RCE) flaw in the MyBB forum software installer. It affects versions 1.8.13 to 1.8.40. The installer fails to properly escape user-supplied database configuration values when writing them to the configuration file. This allows PHP code injection, which can lead to remote code execution if the installer is accessible.

Detection Guidance

To detect this vulnerability, check if your MyBB installation version is between 1.8.13 and 1.8.39. Verify if the installer module (install/index.php) is accessible on your server. Inspect the installer's handling of database configuration inputs for improper escaping of single quotes.

Impact Analysis

An attacker could exploit this to execute arbitrary code on the server running the MyBB installer. This could lead to full system compromise, data theft, or further network infiltration. The impact is severe due to the high CVSS score of 9.8, indicating low attack complexity and high potential damage.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR and HIPAA requirements for data protection. Organizations using vulnerable MyBB versions may face compliance breaches, legal penalties, and reputational damage due to potential data exposure or loss.

Mitigation Strategies

Immediately upgrade MyBB to version 1.8.40 or later. Remove or restrict access to the installer module (install/index.php) if it is not needed. Ensure all database configuration inputs are properly escaped to prevent PHP code injection.

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