CVE-2025-55013 is a relative path traversal vulnerability identified in the Assemblyline 4 Service Client component of the Assemblyline 4 malware analysis framework developed by CybercentreCanada. This vulnerability affects versions prior to 4.6.1.dev138. The Assemblyline 4 Service Client (specifically in the task_handler.py module) interacts with the Assemblyline 4 API to fetch tasks and publish results. It accepts a SHA-256 hash value from the service server and uses this value directly as a local filename when saving files. However, the client does not properly sanitize or validate this input, allowing a malicious or compromised server—or a man-in-the-middle (MITM) attacker capable of intercepting and manipulating communications—to supply a crafted path traversal payload such as '../../../etc/cron.d/evil'. This payload causes the client to write downloaded content to arbitrary locations on the local filesystem, outside the intended directory. This can lead to unauthorized file creation or overwriting critical system files, potentially enabling privilege escalation or persistent malicious code execution. The vulnerability is classified under CWE-23 (Relative Path Traversal). It has a CVSS v3.1 base score of 4.2 (medium severity), with attack vector as adjacent network (AV:A), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no confidentiality impact (C:N), low integrity impact (I:L), and low availability impact (A:L). There are no known exploits in the wild at the time of publication, and the issue is fixed in version 4.6.1.dev138. The vulnerability primarily impacts organizations using vulnerable versions of Assemblyline 4 Service Client, especially those relying on untrusted or potentially compromised Assemblyline servers or operating in environments susceptible to MITM attacks.

For European organizations, the impact of CVE-2025-55013 depends on the deployment and trust model of Assemblyline 4 within their security infrastructure. Assemblyline is used for automated malware analysis and threat intelligence, often in SOCs, CERTs, and security research environments. Exploitation could allow an attacker controlling or intercepting the Assemblyline server-client communication to write arbitrary files on the client system. This could lead to integrity compromise of the analysis environment, enabling attackers to implant backdoors, disrupt malware analysis workflows, or escalate privileges if critical system files are overwritten. Although the confidentiality impact is rated none, the integrity and availability impacts, while low, could disrupt security operations and reduce trust in threat intelligence outputs. European organizations with strict regulatory requirements for system integrity and incident response may face operational risks and compliance challenges if such a vulnerability is exploited. The medium severity rating reflects the complexity of attack (adjacent network with high complexity) and the requirement that the attacker must control or intercept the server-client communication channel. However, in environments where Assemblyline servers are exposed or communications are not properly secured (e.g., lacking TLS or vulnerable to MITM), the risk increases. The lack of known exploits in the wild suggests limited immediate threat but does not preclude targeted attacks against high-value European targets such as critical infrastructure operators, government CERTs, or large enterprises using Assemblyline for malware analysis.

European organizations should take the following specific mitigation steps: 1) Upgrade all Assemblyline 4 Service Client deployments to version 4.6.1.dev138 or later, where the vulnerability is fixed. 2) Ensure that all communications between Assemblyline clients and servers are encrypted and authenticated using strong TLS configurations to prevent MITM attacks. 3) Implement strict network segmentation and access controls to limit exposure of Assemblyline servers and clients to trusted networks only. 4) Employ file system monitoring and integrity checking on systems running Assemblyline clients to detect unauthorized file writes or modifications, particularly outside expected directories. 5) Review and harden the configuration of Assemblyline deployments to minimize privileges of the service client process, reducing potential impact of arbitrary file writes. 6) Conduct regular security audits and penetration testing focusing on the Assemblyline infrastructure to identify potential weaknesses in deployment and communication security. 7) Educate security teams about the risks of path traversal vulnerabilities and the importance of validating all inputs from external services, even trusted ones. These measures go beyond generic patching advice by emphasizing secure deployment architecture, communication security, and active monitoring tailored to the Assemblyline environment.