CVE-2026-45123 | BDVDB-2026-360835 Detail

mybbmybb

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.

Impact#

Per CVSS v3.1: confidentiality impact low, integrity impact none, availability impact none. Attack vector: network.

Weaknesses#

CWE-918 Server-Side Request Forgery (SSRF)

References#

Exploit#

No public exploit known

History#

Version 12026-08-18Record published in the CVE List.

Published

Published: 2026-08-18
Last modified: 2026-08-18

Vendor information

Vendor: mybb
Product: mybb

All mybb vulnerabilities

Score

4.3 Medium

EPSS

less than 1%, Very Low

Estimated chance of exploitation in the next 30 days. EPSS percentile: 30.9.

KEV

Not listed in the CISA Known Exploited Vulnerabilities catalog.

Impact

Server-Side Request Forgery

Action

No specific action is recorded in the source data. Check the references for vendor guidance.

Affected Systems

Vulnerable
< 1.8.40
Fixed
Not stated

Scoring System

CVSS v4.0

Not available

CVSS v3.1

4.3 Medium

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

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

CVSS v3.0

Not available

CVSS v2

Not available

Source: CVE List v5 (record); CISA KEV (kev, action); FIRST EPSS (epss).