CVE-2025-55013: 
Python vulnerability analysis and mitigation

The Assemblyline 4 Service Client (CVE-2025-55013) is affected by a path traversal vulnerability that could lead to arbitrary file writes. The vulnerability exists in versions below 4.6.1.dev138, where the service client accepts a SHA-256 value returned by the service server and uses it directly as a local filename without proper validation. This vulnerability was discovered and disclosed in August 2025 (GitHub Advisory).

The vulnerability exists in the taskhandler.py file within the downloadfile() function, where the SHA-256 string from the service-server JSON response is used as a filename without validation or sanitization. The vulnerability has been assigned a CVSS v3.1 base score of 10.0 (Critical) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H. The issue is classified as CWE-23 (Relative Path Traversal) (GitHub Advisory, NVD).

A successful exploitation of this vulnerability could allow an attacker to write files to arbitrary locations on the disk. This could lead to integrity compromise through overwriting critical files, availability issues through disk space exhaustion, and potential code execution by dropping malicious cron jobs, systemd units, or overwriting binaries. For example, an attacker could write to sensitive locations like '/etc/cron.d/evil' (GitHub Advisory).

The vulnerability has been fixed in version 4.6.1.dev138. The fix includes implementing proper validation of SHA-256 values using regular expressions before using them as filenames. It's important to note that in production environments, this code should be executed within a containerized environment such as assemblyline-v4-service, which ensures filesystem-level permissions and proper network policies (GitHub Advisory).