CVE-2023-27534 is a high-severity path traversal vulnerability (CWE-22) identified in the SFTP implementation of curl versions prior to 8.0.0. The flaw arises from improper handling of the tilde (~) character when it is used as a prefix in the first path element of an SFTP URL or command. Normally, the tilde character is interpreted as a shorthand for the user's home directory on the remote server. However, due to this vulnerability, curl incorrectly replaces the tilde in certain contexts, such as when it appears in a path like /~2/foo. This improper replacement can be exploited by an attacker to bypass path filtering mechanisms or to craft paths that lead to unauthorized file access or manipulation on the remote server. The vulnerability requires that the attacker have some level of privileges (PR:L in CVSS), but no user interaction is needed, and the attack can be performed remotely over the network (AV:N). The impact includes potential full compromise of confidentiality, integrity, and availability of data accessed via the vulnerable curl client when interacting with SFTP servers. The vulnerability was fixed in curl version 8.0.0, and no known exploits are currently reported in the wild. The CVSS v3.1 base score is 8.8, reflecting the high impact and relatively low complexity of exploitation. This vulnerability is particularly relevant for environments where curl is used to automate or script SFTP file transfers, especially in contexts where path validation or filtering is relied upon for security controls.

For European organizations, the impact of CVE-2023-27534 can be significant, especially for enterprises and government agencies that rely on curl for automated SFTP file transfers in their IT infrastructure. Exploitation could allow attackers to bypass path restrictions, potentially accessing sensitive files outside intended directories, leading to data breaches or unauthorized data modification. This could affect confidentiality by exposing sensitive information, integrity by allowing unauthorized file changes, and availability if critical files are deleted or corrupted. Organizations using older versions of curl in DevOps pipelines, backup systems, or data synchronization tasks are at risk. The vulnerability could also be leveraged in supply chain attacks if attackers manipulate file paths during automated deployments. Given the high CVSS score and the widespread use of curl in Linux-based systems common in European data centers, the threat could disrupt critical services or lead to regulatory non-compliance under GDPR if personal data is exposed.

1. Immediate upgrade to curl version 8.0.0 or later, where the vulnerability is fixed, is the most effective mitigation. 2. Audit all systems and scripts that use curl for SFTP transfers to identify and remediate usage of vulnerable versions. 3. Implement strict server-side path validation and access controls on SFTP servers to prevent unauthorized path traversal, regardless of client behavior. 4. Employ network-level monitoring to detect anomalous SFTP requests that include suspicious path patterns such as those exploiting tilde misuse. 5. Use application-layer firewalls or intrusion detection systems with updated signatures to detect attempts to exploit this vulnerability. 6. For environments where immediate upgrade is not feasible, consider restricting SFTP access to trusted users and hosts, and enforce least privilege on file system permissions to limit impact. 7. Conduct security awareness and training for DevOps and system administrators to recognize and remediate vulnerable curl usage in automation scripts.