MyBB up to 1.8.39 Remote Requests Feature inc/functions.php fetch_remote_file server-side request forgery

Summaryinfo

A vulnerability classified as problematic was found in MyBB up to 1.8.39. The affected element is the function fetch_remote_file of the file inc/functions.php of the component Remote Requests Feature. Executing a manipulation can lead to server-side request forgery. The identification of this vulnerability is CVE-2026-45123. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in MyBB up to 1.8.39. It has been declared as problematic. This vulnerability affects the function fetch_remote_file of the file inc/functions.php of the component Remote Requests Feature. The manipulation with an unknown input leads to a server-side request forgery vulnerability. The CWE definition for the vulnerability is CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-45123 since 05/08/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/18/2026).

By approaching the search of inurl:inc/functions.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 1.8.40 eliminates this vulnerability.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Content Management System

Name

• MyBB

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.8.6
• 1.8.7
• 1.8.8
• 1.8.9
• 1.8.10
• 1.8.11
• 1.8.12
• 1.8.13
• 1.8.14
• 1.8.15
• 1.8.16
• 1.8.17
• 1.8.18
• 1.8.19
• 1.8.20
• 1.8.21
• 1.8.22
• 1.8.23
• 1.8.24
• 1.8.25
• 1.8.26
• 1.8.27
• 1.8.28
• 1.8.29
• 1.8.30
• 1.8.31
• 1.8.32
• 1.8.33
• 1.8.34
• 1.8.35
• 1.8.36
• 1.8.37
• 1.8.38
• 1.8.39

License

• open-source

Website

• Product: https://mybb.com/

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