Mail header injection via unsanitized sender name
Published Aug 18, 2026 · Updated Aug 18, 2026
Mail header injection in MyBB before 1.8.40 allows attackers to inject arbitrary email headers via crafted sender names. The Email User controller in member.php?action=do_emailuser accepts fromname from guests or a stored username from permitted users, builds a name string, and passes it to the PHP mail handler without neutralizing CRLF before Return-Path and Reply-To headers are composed. Exposure requires the cansendemail permission and the default PHP mail handler; published records describe header injection only, with no disclosed code execution path.
Summary
What happened
Mail header injection in MyBB before 1.8.40 allows attackers to inject arbitrary email headers via crafted sender names. The Email User controller in member.php?action=do_emailuser accepts fromname from guests or a stored username from permitted users, builds a name string, and passes it to the PHP mail handler without neutralizing CRLF before Return-Path and Reply-To headers are composed. Exposure requires the cansendemail permission and the default PHP mail handler; published records describe header injection only, with no disclosed code execution path.
The record
- CVE
- CVE-2026-45125
- Published
- Aug 18, 2026
- Updated
- Aug 18, 2026
- Vendor
- MyBB
- Product
- MyBB
- Classifications
- CWE-93
- Attack vector
- network
- Privileges
- Unavailable
Timeline
How it unfolded
- Aug 18, 2026CVE publishedPublication date reported by the CVE source.
- Aug 18, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 1.8.40
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo