CVE-2026-45123
Description
MyBB is free and open source forum software. Prior to 1.8.40, the remote requests feature does not correctly handle IPv6 addresses, resulting in a server-side request forgery vulnerability. The default disallowed remote hosts list does not include IPv6 addresses. Verification in fetch_remote_file() fails open when get_ip_by_hostname() returns no result because that function does not return IPv6 results, allowing a crafted remote target to bypass the host restriction. The uniquely identifying implementation details include fail-open verification, and inc/functions.php. This issue is fixed in version 1.8.40.
How to fix
Sources list no fixed version or patch link for this vulnerability.
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mybb mybb | < 1.8.40 | — |
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