CVE-2026-45125

Summary

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.

Affected Software

Weaknesses

• CWE-93: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

References

• https://github.com/mybb/mybb/security/advisories/GHSA-f626-53q9-pqm9
• https://github.com/mybb/mybb/commit/5046c56b515d4593297a4f65b0c6ccb0b55baa01
• https://github.com/mybb/mybb/releases/tag/mybb_1840
• https://mybb.com/versions/1.8.40

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