CVE-2025-11065 identifies a vulnerability in the mapstructure/v2 Go library, widely used for decoding and processing structured data into Go structs. The issue resides in the WeakDecode function, which processes user-supplied input fields. When malformed or crafted inputs are provided, the function generates error messages that inadvertently include sensitive data from the input. This leads to information disclosure, as these detailed error messages may be logged or displayed in security-critical contexts, potentially exposing confidential information such as credentials, tokens, or personal data. The vulnerability can be triggered remotely without authentication but requires user interaction to supply the malformed input. The CVSS 3.1 base score is 5.3, reflecting a medium severity due to the network attack vector, high complexity, no privileges required, and user interaction needed. The impact is limited to confidentiality, with no effect on integrity or availability. No public exploits have been reported yet, but the risk exists especially in applications that do not sanitize error outputs or expose detailed logs to untrusted users. The vulnerability was reserved in late 2025 and published in early 2026, indicating recent discovery and disclosure. No official patches or mitigations are linked yet, so users must apply best practices to limit exposure.

For European organizations, the primary impact is the risk of sensitive information leakage through error messages generated by applications using the vulnerable mapstructure library. This can lead to exposure of confidential data, which may facilitate further attacks such as credential theft or social engineering. Organizations in sectors handling sensitive data—financial services, healthcare, government, and critical infrastructure—are particularly at risk if they use Go-based applications incorporating this library. The vulnerability does not allow code execution or denial of service, but information disclosure can undermine trust, violate data protection regulations like GDPR, and cause reputational damage. Since exploitation requires user interaction, the risk is somewhat mitigated, but automated or targeted attacks could still leverage this flaw. The medium CVSS score reflects moderate risk but should not be underestimated in environments processing sensitive inputs.

1. Monitor for updates from the maintainers of github.com/go-viper/mapstructure/v2 and apply patches promptly once available. 2. Implement input validation and sanitization to prevent malformed data from reaching the WeakDecode function. 3. Suppress or sanitize error messages in production environments to avoid leaking sensitive information; avoid logging detailed error outputs accessible to untrusted users. 4. Employ application-layer firewalls or input filtering to detect and block suspicious malformed inputs targeting this vulnerability. 5. Conduct code reviews and security testing focusing on error handling and data exposure in applications using this library. 6. Educate developers on secure error handling practices, emphasizing the risks of detailed error messages in security-critical contexts. 7. If immediate patching is not possible, consider isolating vulnerable components or restricting access to interfaces that process user-supplied data through this library.