CVE-2025-6499 is a heap-based buffer overflow vulnerability found in the libucl library, specifically affecting versions up to 0.9.2 (including 0.9.0, 0.9.1, and 0.9.2). The vulnerability resides in the function ucl_parse_multiline_string within the src/ucl_parser.c source file. This function is responsible for parsing multiline strings in the Universal Configuration Language (UCL) format. Due to improper handling of input data, an attacker with local access can manipulate the input to trigger a heap-based buffer overflow condition. This can lead to memory corruption, potentially allowing an attacker to crash the application or execute arbitrary code with the privileges of the affected process. The attack vector requires local access with low privileges (PR:L) and does not require user interaction (UI:N). The vulnerability does not affect confidentiality, integrity, or availability directly but can lead to partial availability impact (VA:L) due to potential crashes or memory corruption. 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 exploits in the wild have been reported yet. The vulnerability is classified as problematic, meaning it is significant but not critical. Since the attack requires local access, remote exploitation is not feasible without prior compromise. The libucl library is commonly used in configuration parsing for various software projects, including some Linux-based systems and network appliances, which may incorporate it for configuration management. However, the lack of patch links suggests that fixes may not yet be widely available or distributed at the time of this report.

For European organizations, the impact of CVE-2025-6499 depends largely on the deployment of libucl in their software stacks. Organizations using software that relies on libucl for configuration parsing—particularly in Linux-based environments, embedded systems, or network devices—may be vulnerable if they run affected versions. The local attack requirement limits the threat to insiders or attackers who have already gained some level of access to the system. However, successful exploitation could lead to denial of service through application crashes or potentially privilege escalation if combined with other vulnerabilities. This could disrupt critical services, especially in sectors relying heavily on Linux infrastructure such as telecommunications, finance, and government. The medium severity rating reflects moderate risk, but the public disclosure of the exploit code increases the urgency for mitigation. European organizations with strict security policies and segmented networks may contain the risk more effectively, but those with less controlled internal access or legacy systems may face higher exposure. The vulnerability does not directly compromise confidentiality or integrity but can affect availability and system stability.

Identify all instances of libucl usage within your environment, including embedded systems, network appliances, and Linux-based servers. Upgrade libucl to a version later than 0.9.2 once a patched release is available from the vendor or maintainers. Monitor official repositories and vendor advisories for patch announcements. If immediate patching is not possible, restrict local access to systems running vulnerable libucl versions by enforcing strict access controls and limiting user privileges. Implement application whitelisting and runtime protection mechanisms to detect and prevent anomalous behavior that could indicate exploitation attempts. Conduct internal audits and penetration tests focusing on local privilege escalation and buffer overflow vectors to identify potential exploitation paths. Educate system administrators and users about the risks of local exploitation and the importance of maintaining updated software components. Consider deploying host-based intrusion detection systems (HIDS) that can monitor heap corruption or unusual process crashes related to libucl usage. Isolate critical systems that use libucl in separate network segments to reduce the risk of lateral movement by attackers with local access.