{"id":"CVE-2026-45123","title":"MyBB is free and open source forum software","summary":"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 n…","severity":"medium","cvss":4.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","cwe":["CWE-918"],"published":"2026-08-18","updated":"2026-09-08","sourceUpdated":"2026-09-08T21:02:26.047","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-45123","references":[{"url":"https://github.com/mybb/mybb/commit/9cdadbf66f4cef50019f13aaa8e3470ea6535cb7","label":"security-advisories@github.com"},{"url":"https://github.com/mybb/mybb/releases/tag/mybb_1840","label":"security-advisories@github.com"},{"url":"https://github.com/mybb/mybb/security/advisories/GHSA-56wr-64wx-5g7j","label":"security-advisories@github.com"},{"url":"https://mybb.com/versions/1.8.40","label":"security-advisories@github.com"}],"tags":["nvd"],"epss":0.00269,"epssPercentile":0.19335,"ingestedAt":"2026-09-08T21:11:12.280Z","slug":"CVE-2026-45123","body":"## Overview\n\nMyBB 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":24,"depthScoreParts":{"impact":23.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}