CVE-2025-6856 is a use-after-free vulnerability identified in the HDF5 library version 1.14.6, specifically within the function H5FL__reg_gc_list located in the source file src/H5FL.c. HDF5 (Hierarchical Data Format version 5) is a widely used data model, library, and file format for storing and managing large and complex data collections, commonly utilized in scientific computing, engineering, and data analytics. The vulnerability arises due to improper memory management where a pointer is used after the memory it references has been freed, leading to undefined behavior. This can cause application crashes, data corruption, or potentially allow an attacker to execute arbitrary code or escalate privileges. The vulnerability requires local access to the system (local attack vector) and low complexity to exploit, with no user interaction or authentication needed beyond local privileges. The CVSS 4.0 base score is 4.8, indicating a medium severity level. The exploit has been publicly disclosed, increasing the risk of exploitation, although no known active exploitation in the wild has been reported yet. The vulnerability does not affect confidentiality, integrity, or availability directly but poses a risk of privilege escalation or denial of service through memory corruption. The lack of a patch link suggests that a fix may not yet be publicly available or is pending release.

For European organizations, the impact of this vulnerability depends largely on their use of the HDF5 library in local applications or systems. Organizations involved in scientific research, engineering, finance, and data analytics that rely on HDF5 for data storage and processing are at risk. Exploitation could lead to local privilege escalation or denial of service, potentially disrupting critical data processing workflows or enabling attackers to gain higher system privileges. This could compromise sensitive research data or intellectual property, especially in sectors like pharmaceuticals, aerospace, and energy. Since exploitation requires local access, the threat is more significant in environments where multiple users share systems or where attackers can gain initial footholds via other means. The public disclosure of the exploit increases the urgency for European organizations to assess and mitigate the risk promptly to avoid lateral movement or escalation within their networks.

European organizations should take the following specific steps: 1) Identify all systems and applications using HDF5 version 1.14.6 and assess their exposure to local users. 2) Restrict local access to trusted users only and enforce strict access controls and user privilege separation to minimize the risk of exploitation. 3) Monitor for unusual application crashes or behavior that could indicate exploitation attempts. 4) Apply any available patches or updates from the HDF5 maintainers as soon as they are released; if no patch is available, consider downgrading to a previous stable version or upgrading to a newer version if it is confirmed safe. 5) Implement host-based intrusion detection systems (HIDS) to detect anomalous memory usage or exploitation patterns. 6) Educate local users about the risks of executing untrusted code or files that might trigger the vulnerability. 7) For critical systems, consider sandboxing or isolating applications using HDF5 to limit the impact of potential exploitation.