CVE-2025-29459 is a high-severity vulnerability affecting MyBB forum software version 1.8.38. The issue arises from the Mail function within MyBB, which allows a remote attacker with at least board administrator privileges to perform actions that could lead to the disclosure of sensitive information. The vulnerability is categorized under CWE-918, which corresponds to Server-Side Request Forgery (SSRF). SSRF vulnerabilities enable an attacker to induce the server to make HTTP requests to arbitrary domains, potentially accessing internal resources or sensitive data not otherwise exposed. In this case, the Mail function's implementation may allow an attacker to craft requests that bypass existing SSRF mitigations, exploiting the allowed actions of board administrators to extract sensitive information. The supplier disputes the severity of this vulnerability, arguing that the allowed actions of board administrators and existing SSRF mitigations reduce the risk. However, the CVSS v3.1 base score is 7.6 (high), reflecting the vulnerability's potential to impact confidentiality (high), integrity (low), and availability (low). The attack vector is network-based (AV:N), with low attack complexity (AC:L), requiring privileges (PR:L) but no user interaction (UI:N), and the scope remains unchanged (S:U). No known exploits are currently reported in the wild, and no patches or vendor advisories have been published yet. The vulnerability was reserved in March 2025 and published in April 2025. Given the nature of MyBB as a widely used open-source forum platform, this vulnerability could affect numerous organizations relying on MyBB for community engagement or internal communication, especially if board administrator accounts are compromised or misused.

For European organizations using MyBB 1.8.38, this vulnerability poses a significant risk to the confidentiality of sensitive information. Attackers with board administrator privileges could exploit the Mail function to perform SSRF attacks, potentially accessing internal systems or data that should be protected. This could lead to unauthorized disclosure of personal data, intellectual property, or internal communications, which is particularly critical under the GDPR regulatory framework in Europe. The integrity and availability impacts are assessed as low, but the confidentiality breach alone can result in regulatory penalties, reputational damage, and loss of customer trust. Organizations with public-facing MyBB forums or those that use MyBB for internal collaboration are at higher risk. The requirement for board administrator privileges limits the attack surface but does not eliminate risk, as credential compromise or insider threats could enable exploitation. The absence of known exploits in the wild suggests that immediate widespread attacks are unlikely, but the high CVSS score indicates that once exploit code becomes available, rapid exploitation could occur. European organizations should prioritize assessing their MyBB deployments, especially those with sensitive data exposure, to mitigate potential impacts.

1. Restrict and monitor board administrator privileges rigorously to minimize the risk of credential compromise or misuse. Implement strong authentication mechanisms such as multi-factor authentication (MFA) for all administrator accounts. 2. Review and harden the Mail function configuration and usage within MyBB to ensure it cannot be abused for SSRF attacks. This may include disabling or restricting mail features that allow arbitrary URL requests or external resource fetching. 3. Implement network-level controls such as egress filtering and internal firewall rules to prevent the MyBB server from making unauthorized outbound requests, especially to internal or sensitive network segments. 4. Conduct regular security audits and code reviews focusing on SSRF mitigations and the Mail function's handling of URLs and external inputs. 5. Monitor logs for unusual outbound requests originating from the MyBB server or anomalous mail function usage patterns. 6. Stay updated with vendor advisories and apply patches promptly once available. 7. Consider isolating MyBB instances in segmented network zones to limit potential lateral movement in case of exploitation. 8. Educate board administrators on phishing and social engineering risks to reduce the likelihood of credential compromise.