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CVE-2026-45123

4.3 · MEDIUM

MyBB is free and open source forum software.

Published Aug 18, 2026CWE-918EPSS 0.37%

Overview

CVE-2026-45123 is a medium-severity vulnerability. It was published on August 18, 2026 and has a CVSS 3.1 base score of 4.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/mybb/mybb/commit/9cdadbf66f4cef50019f13aaa8e3470ea6535cb7GitHubgithub.com/mybb/mybb/releases/tag/mybb_1840GitHubgithub.com/mybb/mybb/security/advisories/GHSA-56wr-64wx-5g7jRefmybb.com/versions/1.8.40

How CyberStrike helps

Frequently asked questions

What is CVE-2026-45123?

CVE-2026-45123 is a medium-severity vulnerability. It was published on August 18, 2026 and has a CVSS 3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2026-45123?

This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-45123?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-45123?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-45123 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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