# CVE-2026-45118

## Summary

- **CVE ID:** CVE-2026-45118
- **Severity:** CRITICAL
- **CVSS Score:** 9.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N)
- **CWE:** CWE-83
- **Published:** Aug 18, 2026
- **Last Modified:** Aug 18, 2026

## Description

MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input['from'] or the Referer HTTP header in $_SERVER['HTTP_REFERER'] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the `Click here if you don't want to wait any longer` link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.

## Affected Products

- mybb — mybb (< 1.8.40)

## References

- [CNA](https://github.com/mybb/mybb/security/advisories/GHSA-wf92-5q5h-qr53)
- [CNA](https://github.com/mybb/mybb/releases/tag/mybb_1840)
- [CNA](https://mybb.com/versions/1.8.40)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.38%
- **EPSS Percentile:** 31.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._