CVE-2026-45123Network attack vector

Authenticated SSRF via IPv6 host bypass

Published Aug 18, 2026 · Updated Aug 18, 2026

Server-side request forgery in MyBB before 1.8.40 allows remote authenticated users to reach disallowed hosts via IPv6 targets. In inc/functions.php, fetch_remote_file() fails open when get_ip_by_hostname() returns no result, and the default disallowed remote-host list does not cover IPv6 addresses, so crafted IPv6 destinations bypass host validation. Exploitation requires an authenticated code path that invokes the remote requests feature; the published scoring indicates limited confidentiality and integrity impact rather than unrestricted server compromise.

CVSS severity4.3
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Server-side request forgery in MyBB before 1.8.40 allows remote authenticated users to reach disallowed hosts via IPv6 targets. In inc/functions.php, fetch_remote_file() fails open when get_ip_by_hostname() returns no result, and the default disallowed remote-host list does not cover IPv6 addresses, so crafted IPv6 destinations bypass host validation. Exploitation requires an authenticated code path that invokes the remote requests feature; the published scoring indicates limited confidentiality and integrity impact rather than unrestricted server compromise.

The record

CVE
CVE-2026-45123
Published
Aug 18, 2026
Updated
Aug 18, 2026
Vendor
MyBB
Product
MyBB
Classifications
CWE-918, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.8.40

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MyBB · MyBBversion=< 1.8.40

Published CVSS scores

4.3MyBBCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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