CVE-2021-3998 is a high-severity vulnerability identified in the GNU C Library (glibc), specifically affecting versions 2.33 and above. The flaw resides in the realpath() function, which is responsible for resolving absolute file paths by canonicalizing symbolic links, relative paths, and redundant separators. Due to an out-of-bounds read condition (classified under CWE-125), realpath() can return unexpected values. This behavior can lead to the leakage of sensitive information from memory, as the function may read beyond the intended buffer boundaries and disclose data that should remain protected. The vulnerability does not require any privileges or user interaction to be exploited, and it can be triggered remotely if an attacker can influence the input to realpath(). The CVSS v3.1 base score is 7.5, reflecting a high severity level primarily due to the confidentiality impact (high), with no impact on integrity or availability. Although no known exploits are currently reported in the wild, the vulnerability poses a significant risk because glibc is a core component widely used in Linux-based systems, including servers, desktops, and embedded devices. Exploiting this flaw could allow attackers to gain unauthorized access to sensitive data residing in memory, potentially including cryptographic keys, passwords, or other confidential information processed by applications relying on glibc's realpath().

For European organizations, the impact of CVE-2021-3998 can be substantial given the widespread use of glibc in Linux environments across government, finance, healthcare, telecommunications, and critical infrastructure sectors. Information leakage could lead to exposure of sensitive personal data protected under GDPR, intellectual property, or security credentials, increasing the risk of further attacks such as privilege escalation or lateral movement within networks. Organizations running vulnerable versions of glibc on their servers or endpoints may inadvertently expose confidential information to attackers capable of manipulating file path inputs. This is particularly concerning for cloud service providers and data centers in Europe that host multi-tenant environments where isolation between tenants is critical. The vulnerability's ease of exploitation without authentication or user interaction further elevates the risk profile, making it a viable vector for automated scanning and exploitation attempts. Although no active exploits are currently known, the potential for future weaponization necessitates proactive mitigation to protect sensitive European digital assets and comply with stringent data protection regulations.

To mitigate CVE-2021-3998 effectively, European organizations should prioritize the following actions: 1) Immediate patching: Upgrade glibc to a version where this vulnerability is fixed (check distributions for updated packages, e.g., glibc 2.34 or later). 2) Audit and monitor: Identify all systems running affected glibc versions, including containers and embedded devices, and monitor logs for suspicious usage of realpath() or unusual file path resolution activities. 3) Restrict input vectors: Harden applications and services that accept file path inputs by validating and sanitizing inputs rigorously to reduce the attack surface. 4) Implement memory protection mechanisms: Use security features such as Address Space Layout Randomization (ASLR) and stack canaries to complicate exploitation attempts. 5) Network segmentation: Limit exposure of vulnerable systems by segmenting networks and restricting access to critical servers. 6) Incident response readiness: Prepare detection and response plans for potential exploitation attempts, including anomaly detection for unexpected memory disclosures. 7) Vendor coordination: Engage with Linux distribution vendors and software suppliers to ensure timely updates and patches are applied across all environments.