CVE-2025-57632 is a high-severity buffer overflow vulnerability affecting libsmb2 version 6.2 and later. libsmb2 is a client library used to implement the SMB2 protocol, which is widely used for file sharing and network communication in various operating systems and applications. The vulnerability arises when libsmb2 processes SMB2 chained Protocol Data Units (PDUs) using the NextCommand field. Specifically, the function smb2_add_iovector() is called repeatedly to append data to a fixed-size iovec array without verifying that the number of vectors (v->niov) does not exceed the maximum allowed (SMB2_MAX_VECTORS=256). This lack of boundary checking allows an attacker to craft malicious SMB2 responses containing an excessive number of chained PDUs, causing the iovec array to overflow. This heap out-of-bounds write leads to memory corruption, which can cause application crashes and potentially allow arbitrary code execution. Furthermore, the vulnerability is exacerbated by the SMB2_OPLOCK_BREAK path, which bypasses message ID validation, potentially enabling attackers to exploit the flaw without proper request-response correlation. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network, making it particularly dangerous. Although no known exploits are currently reported in the wild, the CVSS score of 7.5 (high) reflects the significant risk posed by this vulnerability due to its potential to disrupt availability and compromise system integrity.

For European organizations, this vulnerability poses a substantial risk, especially for those relying on SMB2 for file sharing and network communication, including enterprises, government agencies, and critical infrastructure providers. Exploitation could lead to denial of service through application crashes or, more severely, arbitrary code execution, which could allow attackers to gain control over affected systems. This could result in data loss, disruption of business operations, lateral movement within networks, and potential deployment of ransomware or other malware. Given the SMB protocol's widespread use in Windows environments and various Linux distributions that utilize libsmb2, organizations with mixed or heterogeneous environments are particularly vulnerable. The bypass of message ID validation increases the likelihood of successful exploitation without triggering typical protocol safeguards. Consequently, the vulnerability could be leveraged by threat actors to target sensitive data repositories or disrupt essential services, impacting confidentiality, integrity, and availability.

To mitigate this vulnerability, organizations should prioritize the following actions: 1) Apply patches or updates from libsmb2 maintainers as soon as they become available; since no patch links are currently provided, monitoring official repositories and security advisories is critical. 2) Implement network-level controls to restrict SMB traffic to trusted hosts and segments, using firewalls and network segmentation to limit exposure. 3) Employ intrusion detection and prevention systems (IDS/IPS) with signatures or heuristics capable of detecting anomalous SMB2 chained PDU patterns indicative of exploitation attempts. 4) Disable SMB2 support in clients or servers where it is not required, or consider enforcing SMB3 with enhanced security features. 5) Conduct regular vulnerability scanning and penetration testing focused on SMB services to identify and remediate exposure. 6) Monitor logs for unusual SMB2_OPLOCK_BREAK messages or unexpected protocol behavior that may signal exploitation attempts. 7) Educate IT staff about this vulnerability to ensure rapid response and incident handling. These targeted measures go beyond generic advice by focusing on protocol-specific controls and proactive detection tailored to the nature of the vulnerability.