CVE-2026-45123 MEDIUM

CVE-2026-45123: MyBB: IPv6 SSRF

Vendor Mybb

Product mybb

Weakness CWE-918 · SSRF

Published August 18, 2026

Last update August 18, 2026

View on NVD All CVEs

CVSS base score

4.3/10

Attack vector Network

Attack complexity Low

Privileges required Low

User interaction None

Confidentiality Low

Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

August 18, 2026 CVE published

External resources

03References

NVD — National Vulnerability Database https://nvd.nist.gov/vuln/detail/CVE-2026-45123 CWE — Common Weakness Enumeration https://cwe.mitre.org/data/definitions/918.html AskarLabs — CWE-918 write-up Server-Side Request Forgery

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04Related CVE

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