CVE-2025-29458 is a high-severity vulnerability identified in MyBB version 1.8.38, a widely used open-source forum software. The vulnerability arises from the Change Avatar function, which allows a remote attacker with at least board administrator privileges to exploit a Server-Side Request Forgery (SSRF)-like flaw. Through this flaw, the attacker can coerce the server to make unintended HTTP requests, potentially leading to the disclosure of sensitive information. The vulnerability is classified under CWE-918, indicating improper server-side request handling. Although the supplier disputes the severity due to the requirement of board administrator privileges and existing SSRF mitigations, the CVSS 3.1 score of 7.6 reflects a high impact, with a vector indicating network attack complexity is low, privileges required are low (PR:L), no user interaction is needed, and the impact on confidentiality is high, with limited integrity and availability impact. The vulnerability allows an attacker to extract sensitive data from the server environment or internal network by abusing the avatar upload/change mechanism, which likely processes URLs or external resources. No known exploits are currently in the wild, and no patches have been officially released as of the publication date (April 17, 2025). The vulnerability affects MyBB installations that have the Change Avatar feature enabled and accessible to board administrators, which is typical in many forum deployments. Given the nature of the flaw, exploitation could lead to unauthorized access to internal services, leakage of sensitive configuration or user data, and potential lateral movement within the affected infrastructure.

For European organizations, especially those operating online communities, forums, or customer support platforms using MyBB 1.8.38, this vulnerability poses a significant risk. The high confidentiality impact means sensitive user data, internal network information, or proprietary data could be exposed. This could lead to reputational damage, regulatory non-compliance (e.g., GDPR violations), and potential financial losses. The requirement for board administrator privileges limits the attack surface but does not eliminate risk, as insider threats or compromised administrator accounts could be leveraged. Additionally, the SSRF nature of the vulnerability could be used to pivot attacks into internal networks, potentially compromising other critical systems. Given the widespread use of MyBB in various sectors including education, government, and private enterprises across Europe, the vulnerability could affect a broad range of organizations. The lack of available patches increases the urgency for mitigation. The dispute by the supplier regarding the vulnerability's impact suggests some uncertainty, but the CVSS score and CWE classification indicate a genuine risk that should not be ignored.

Restrict board administrator privileges strictly to trusted personnel and enforce strong authentication mechanisms, including multi-factor authentication, to reduce the risk of credential compromise. Temporarily disable the Change Avatar function or restrict it to trusted IP ranges or VPN access until an official patch is released. Implement network-level controls such as web application firewalls (WAFs) to detect and block SSRF-like request patterns originating from the forum application. Conduct thorough logging and monitoring of avatar change requests and related server-side HTTP requests to detect anomalous activity indicative of exploitation attempts. Isolate the MyBB server within a segmented network zone with limited access to internal resources to minimize potential lateral movement if exploitation occurs. Engage in proactive vulnerability scanning and penetration testing focused on SSRF and related vulnerabilities within the MyBB environment. Stay informed on vendor updates and apply patches immediately once available, and consider upgrading to newer MyBB versions if they address this vulnerability. Review and harden server-side request handling code or configurations related to avatar uploads, such as validating and sanitizing URLs or disabling external resource fetching if feasible.