CVE-2018-20325

Vulnerability

The definitions Python package (all versions prior to a fix) contains a vulnerability in the load() method in definitions/parser.py. The method processes YAML definitions without proper sanitization, allowing arbitrary Python code execution when deserializing untrusted YAML data. This is due to the use of eval() or similar unsafe deserialization. Affected versions: all versions up to the fix (no fixed version disclosed in available references). [1][2]

Exploitation

An attacker needs to supply a malicious YAML definition file to an application using the vulnerable definitions.load() function. No authentication or special privileges are required if the attacker can provide the input. The attack vector is network-based (remote). The attacker crafts a YAML file that includes Python expressions or commands, which are executed during deserialization. [3]

Impact

Successful exploitation allows arbitrary command execution on the server or client system processing the YAML. This can lead to full compromise of the system, including data disclosure, modification, or denial of service. The privilege level depends on the context of the application; if run with elevated privileges, the attacker gains those privileges. [1][4]

Mitigation

No official patch or fixed version has been released by the package maintainer as of the publication date (2018-12-21). The recommended mitigation is to avoid using the definitions package with untrusted YAML input. If possible, switch to a safer alternative for YAML parsing and schema validation. The vulnerability is recorded in the PySec advisory database. [4]