Medium 5.3Published Aug 18, 2026

CVE-2026-45125MyBB: Email User CRLF injection

Updated under an hour ago (2026-10-19 09:50 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

MyBB is free and open source forum software. Prior to 1.8.40, the Email User controller does not sanitize sender names correctly, resulting in mail header injection. member.php?action=do_emailuser accepts the fromname HTTP parameter for guests or the stored username for authenticated users when the cansendemail group permission is enabled. When mail_handler is set to the default PHP mail value, the sender name is used without sanitization in Return-Path and Reply-To headers, allowing arbitrary headers to be injected with CRLF sequences. This issue is fixed in version 1.8.40.

CVSS: 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness (CWE): CWE-93
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Aug 18, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

mybb mybb mybb:mybb (from the name)	before 1.8.40	CNA record

References

https://github.com/mybb/mybb/security/advisories/GHSA-f626-53q9-pqm9x-refsource-confirm
https://github.com/mybb/mybb/commit/5046c56b515d4593297a4f65b0c6ccb0b55baa01x-refsource-misc
https://github.com/mybb/mybb/releases/tag/mybb_1840x-refsource-misc
https://mybb.com/versions/1.8.40x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.