Rule Category

POLICY-OTHER --

Alert Message

POLICY-OTHER PyYAML Python object serialization attempt

Rule Explanation

This rule detects the attempted download of a YAML file that contains a serialized Python object by looking for the syntax used to create a new Python object. This rule is in response to the ability to run arbitrary code via the object deserialization process in PyYAML when loading untrusted YAML files without using a safe YAML load method.

What To Look For

This rule detects the attempted download of a YAML file that contains a serialized Python object.

Known Usage

No public information

False Positives

No known false positives

Contributors

Cisco Talos Intelligence Group

Rule Groups

No rule groups

CVE

Rule Vulnerability

N/A

Not Applicable

CVE Additional Information

CVE-2020-14343
A vulnerability was discovered in the PyYAML library in versions before 5.4, where it is susceptible to arbitrary code execution when it processes untrusted YAML files through the full_load method or with the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable to this flaw. This flaw allows an attacker to execute arbitrary code on the system by abusing the python/object/new constructor. This flaw is due to an incomplete fix for CVE-2020-1747.
Details
Severity Base Score9.8
Impact Score5.9 Exploit Score3.9
Confidentiality ImpactHIGH Integrity ImpactHIGH
Availability ImpactHIGH Attack VectorNETWORK
ScopeUNCHANGED User InteractionNONE
Authentication Ease of AccessLOW
Privileges RequiredNONE
CVE-2020-1747
A vulnerability was discovered in the PyYAML library in versions before 5.3.1, where it is susceptible to arbitrary code execution when it processes untrusted YAML files through the full_load method or with the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable to this flaw. An attacker could use this flaw to execute arbitrary code on the system by abusing the python/object/new constructor.
Details
Severity Base Score9.8
Impact Score5.9 Exploit Score3.9
Confidentiality ImpactHIGH Integrity ImpactHIGH
Availability ImpactHIGH Attack VectorNETWORK
ScopeUNCHANGED User InteractionNONE
Authentication Ease of AccessLOW
Privileges RequiredNONE

MITRE ATT&CK Framework

Tactic: Execution

Technique: Execution through Module Load

For reference, see the MITRE ATT&CK vulnerability types here: https://attack.mitre.org