CVE-2026-45117 mybb CVE debrief

Who should care

System administrators and security teams responsible for MyBB installations should assess exposure and prioritize remediation. This includes reviewing current MyBB versions, verifying configuration files, and ensuring timely updates to prevent exploitation. Security teams should also monitor system logs for suspicious activity and implement compensating controls where necessary.

Why it matters

CVE-2026-45117 is a critical vulnerability in MyBB forum software that allows for remote code execution. System administrators and security teams should assess exposure and prioritize remediation.

• Remote code execution is possible when the installer is available
• PHP code injection can lead to arbitrary code execution
• System compromise may occur if the vulnerability is exploited
• Verification of MyBB version and configuration is necessary

Technical summary

The MyBB forum software installer module does not properly escape user-supplied database configuration values, allowing for PHP code injection and remote code execution when the installer is available. This issue was introduced in MyBB 1.8.13 and fixed in version 1.8.40. The vulnerability arises from the addcslashes() function's incomplete sanitization due to the missing backslash character in the $characters argument added in MyBB 1.8.13, enabling crafted input to escape and execute PHP code arbitrarily. System administrators should assess exposure and prioritize remediation.

Defensive priority

High

Recommended defensive actions

• Immediately upgrade to MyBB version 1.8.40 or later
• Review and verify the configuration files for any potential PHP code injection
• Monitor the system for suspicious activity
• Restrict access to the installer module
• Perform a thorough review of system logs to detect any signs of exploitation
• Ensure that all MyBB installations are tracked and updated regularly
• Verify the integrity of configuration files to prevent unauthorized modifications

Evidence notes

The vulnerability exists in the installer module of MyBB versions 1.8.13 to 1.8.39. The issue is fixed in version 1.8.40. The CVE record and NVD entry provide details on the vulnerability. Evidence is based on the official CVE Program record and NIST NVD detail page, which confirm the vulnerability's existence and provide source-specific vulnerability assessments.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.