MyBB: IPv6 SSRF

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-45123
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-18 16:17:07 UTC
Updated2026-09-08 21:02:26 UTC
DescriptionMyBB 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

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

EPSS: 0.002690000 probability, percentile 0.188420000 (date 2026-09-08)

Problem Types: CWE-918 | CWE-918 CWE-918: Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
3.1CNADECLARED4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mybb Mybb affected < 1.8.40 Not specified

References

ReferenceSourceLinkTags
github.com/mybb/mybb/security/advisories/GHSA-56wr-64wx-5g7j [email protected] github.com
github.com/mybb/mybb/releases/tag/mybb_1840 [email protected] github.com
mybb.com/versions/1.8.40 [email protected] mybb.com
github.com/mybb/mybb/commit/9cdadbf66f4cef50019f13aaa8e3470ea6535cb7 [email protected] github.com
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