CVE-2025-29460 is a high-severity vulnerability identified in MyBB version 1.8.38, a popular open-source forum software widely used for online community management. The vulnerability arises from the 'Add Mycode' function, which allows board administrators to create custom BBCode tags. This function is intended to extend forum capabilities by enabling administrators to define new markup codes that users can apply in posts. However, the vulnerability enables a remote attacker with board administrator privileges to exploit this feature to obtain sensitive information. The core issue relates to Server-Side Request Forgery (SSRF), classified under CWE-918, where the application can be manipulated to make unauthorized requests to internal or external systems. Although the supplier disputes the severity of this issue, citing the limited scope of actions allowed to board administrators and existing SSRF mitigations, the CVSS 3.1 base score of 7.6 reflects a high risk due to the potential confidentiality impact. The attack vector is network-based (AV:N), requires low attack complexity (AC:L), and privileges at the level of a board administrator (PR:L), but no user interaction is needed (UI:N). The vulnerability affects confidentiality significantly (C:H), with limited impact on integrity (I:L) and availability (A:L). There are no known exploits in the wild, and no patches have been published at the time of this report. The vulnerability's exploitation could allow attackers to access sensitive internal data or services by leveraging the SSRF capability through the Add Mycode function, potentially leading to information disclosure or further internal network reconnaissance.

For European organizations using MyBB 1.8.38 or similar versions, this vulnerability poses a significant risk to the confidentiality of sensitive information hosted on their forums. Since the exploit requires board administrator privileges, the threat is primarily internal or from compromised administrator accounts. Successful exploitation could lead to unauthorized access to internal network resources, exposing sensitive data or enabling lateral movement within the organization's infrastructure. This is particularly critical for organizations that use MyBB forums for customer support, internal communications, or as a platform for sensitive discussions. The limited impact on integrity and availability reduces the risk of data manipulation or service disruption but does not eliminate the threat of data leakage. Given the widespread use of MyBB in various sectors, including education, government, and private enterprises across Europe, the vulnerability could be leveraged in targeted attacks, especially where administrative credentials are weak or compromised. The absence of known exploits in the wild suggests the threat is currently theoretical but could escalate if attackers develop reliable exploitation techniques. The dispute by the supplier regarding the vulnerability's impact indicates that mitigation controls may reduce risk but do not fully eliminate it. Therefore, European organizations should treat this vulnerability seriously, particularly those with high-value data or critical internal services accessible via the forum platform.

1. Restrict Board Administrator Access: Limit the number of users with board administrator privileges to the minimum necessary and enforce strong authentication mechanisms, including multi-factor authentication (MFA), to reduce the risk of credential compromise. 2. Review and Harden Mycode Usage: Audit all custom Mycode definitions to ensure they do not allow unintended SSRF or external requests. Disable or remove any Mycode that can be exploited to perform server-side requests. 3. Network Segmentation and Egress Filtering: Implement strict network segmentation to isolate the forum server from sensitive internal systems. Use egress filtering to prevent the server from making unauthorized outbound requests, mitigating SSRF exploitation. 4. Monitor and Log Administrative Actions: Enable detailed logging of board administrator activities, particularly those involving Mycode creation or modification, to detect suspicious behavior promptly. 5. Apply Principle of Least Privilege: Ensure that the forum software and its underlying server run with the least privileges necessary, limiting the potential impact of exploitation. 6. Stay Updated on Vendor Communications: Monitor MyBB project updates and security advisories for patches or official guidance addressing this vulnerability. 7. Conduct Regular Security Assessments: Perform penetration testing and code reviews focusing on custom Mycode implementations and SSRF vectors. 8. Educate Administrators: Train board administrators on secure Mycode practices and the risks associated with SSRF to prevent inadvertent introduction of vulnerable code.