CVE-2024-23336 in MyBB
Summary
by MITRE • 05/01/2024
MyBB is a free and open source forum software. The default list of disallowed remote hosts does not contain the `127.0.0.0/8` block, which may result in a Server-Side Request Forgery (SSRF) vulnerability. The Configuration File's _Disallowed Remote Addresses_ list (`$config['disallowed_remote_addresses']`) contains the address `127.0.0.1`, but does not include the complete block `127.0.0.0/8`. MyBB 1.8.38 resolves this issue in default installations. Administrators of installed boards should update the existing configuration (`inc/config.php`) to include all addresses blocked by default. Additionally, users are advised to verify that it includes any other IPv4 addresses resolving to the server and other internal resources. Users unable to upgrade may manually add 127.0.0.0/8' to their disallowed address list.
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Analysis
by VulDB Data Team • 06/30/2025
The vulnerability described in CVE-2024-23336 represents a critical Server-Side Request Forgery (SSRF) flaw within MyBB forum software, a widely deployed open source discussion platform. This vulnerability stems from an incomplete security configuration in the default installation, specifically within the disallowed remote addresses list that controls outbound network requests from the server. The flaw occurs because the configuration file's Disallowed Remote Addresses array contains the specific address 127.0.0.1 but fails to include the broader 127.0.0.0/8 CIDR block, which encompasses all loopback addresses within the 127.x.x.x range. This incomplete blocking mechanism creates a significant security gap that allows attackers to potentially bypass intended network restrictions and make unauthorized requests to internal server resources that should remain protected from external access.
The technical implementation of this vulnerability involves the MyBB software's handling of remote URL validation during outbound requests, where the software relies on a predefined list of disallowed IP address ranges to prevent access to internal network resources. When the configuration does not include the 127.0.0.0/8 block, an attacker can exploit this gap by crafting requests that target addresses within this range, effectively allowing the server to make requests to localhost services or internal network resources that should be restricted. This vulnerability directly maps to CWE-918, which specifically addresses Server-Side Request Forgery vulnerabilities, and aligns with ATT&CK technique T1071.004 for application layer protocol traffic shaping. The flaw is particularly dangerous because it can enable attackers to access internal services, databases, or administrative interfaces that are typically only accessible from within the server's local network, potentially leading to privilege escalation or data exfiltration.
The operational impact of this vulnerability extends beyond simple network access bypass, as it creates opportunities for attackers to perform reconnaissance on internal server services, exploit other vulnerabilities in internal applications, or gain access to sensitive information that should remain isolated from external networks. Attackers could leverage this flaw to probe internal systems, potentially identifying running services, weak configurations, or other vulnerable components that exist within the server's local network environment. The vulnerability affects all MyBB installations that have not been updated to version 1.8.38 or have not manually corrected their configuration files to include the missing 127.0.0.0/8 block. This makes it particularly concerning for organizations with multiple MyBB installations or those that cannot immediately apply the official patch, as the manual correction process requires administrators to properly understand their network configuration and ensure that all potentially dangerous internal IP ranges are properly blocked.
Organizations affected by this vulnerability should implement immediate remediation measures to protect their installations from potential exploitation. The recommended approach involves updating the configuration file inc/config.php to include the 127.0.0.0/8 CIDR block in the disallowed remote addresses list, ensuring that all loopback addresses are properly restricted from external access. Administrators should also perform comprehensive network audits to identify any other internal IPv4 addresses or ranges that might pose similar risks, particularly those that resolve to the server itself or other internal resources. For organizations unable to upgrade to the patched version, manual configuration changes must be carefully implemented to prevent any gaps in protection. The vulnerability demonstrates the critical importance of comprehensive security configuration management and the need for regular security assessments of default installations, as incomplete default security settings can create persistent attack vectors that remain exploitable until properly addressed through either automated updates or manual remediation processes.