CVE-2026-45118Critical· 9.3▾ Midnight

MyBB is free and open source forum software

▾ Midnight zone — Critical, or high with PoC / in-the-wild

Depth score51/ 100 · Moderate

impact 51.2 · likelihood 0.1 · exploitation 0

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Proof of concept

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Published

Aug 18, 2026

Updated

Sep 8, 2026

CVSS

9.3

Vendor

—

Product

—

CWE

CWE-83

Depth score

51 · Moderate

EPSS

0.55% · p46

Platforms

—

Source

NVD

Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS history

Exploit-prediction probability, daily snapshots since Sep 8.

0.4% → 0.5%▲ 0.2%

Timeline

Disclosure to exploitation, from the record and what we observed since indexing it.

4 events · 38 days

Aug 18, 2026Published
Disclosed via NVD
Sep 8, 2026Record revised
Last analysed / modified upstream
Sep 8, 2026EPSS first tracked
0.4%
Sep 25, 2026EPSS peak
0.4% → 0.5%

CWE-83 #nvd

Full technical detail▾

Overview

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.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

References

Related vulnerabilities

Connected by shared product, vendor, weakness, or advisory.

#nvd

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