Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS1tam1qLWo0OHEtOXdnMs4AAwRm

SnakeYaml Constructor Deserialization Remote Code Execution

Summary

SnakeYaml's Constructor class, which inherits from SafeConstructor, allows any type be deserialized given the following line:

new Yaml(new Constructor(TestDataClass.class)).load(yamlContent);

Types do not have to match the types of properties in the target class. A ConstructorException is thrown, but only after a malicious payload is deserialized.

Severity

High, lack of type checks during deserialization allows remote code execution.

Proof of Concept

Execute bash run.sh. The PoC uses Constructor to deserialize a payload
for RCE. RCE is demonstrated by using a payload which performs a http request to
http://127.0.0.1:8000.

Example output of successful run of proof of concept:

$ bash run.sh

[+] Downloading snakeyaml if needed
[+] Starting mock HTTP server on 127.0.0.1:8000 to demonstrate RCE
nc: no process found
[+] Compiling and running Proof of Concept, which a payload that sends a HTTP request to mock web server.
[+] An exception is expected.
Exception:
Cannot create property=payload for JavaBean=Main$TestDataClass@3cbbc1e0
 in 'string', line 1, column 1:
    payload: !!javax.script.ScriptEn ... 
    ^
Can not set java.lang.String field Main$TestDataClass.payload to javax.script.ScriptEngineManager
 in 'string', line 1, column 10:
    payload: !!javax.script.ScriptEngineManag ... 
             ^

	at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.constructJavaBean2ndStep(Constructor.java:291)
	at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.construct(Constructor.java:172)
	at org.yaml.snakeyaml.constructor.Constructor$ConstructYamlObject.construct(Constructor.java:332)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:230)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:220)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructDocument(BaseConstructor.java:174)
	at org.yaml.snakeyaml.constructor.BaseConstructor.getSingleData(BaseConstructor.java:158)
	at org.yaml.snakeyaml.Yaml.loadFromReader(Yaml.java:491)
	at org.yaml.snakeyaml.Yaml.load(Yaml.java:416)
	at Main.main(Main.java:37)
Caused by: java.lang.IllegalArgumentException: Can not set java.lang.String field Main$TestDataClass.payload to javax.script.ScriptEngineManager
	at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
	at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
	at java.base/jdk.internal.reflect.UnsafeObjectFieldAccessorImpl.set(UnsafeObjectFieldAccessorImpl.java:81)
	at java.base/java.lang.reflect.Field.set(Field.java:780)
	at org.yaml.snakeyaml.introspector.FieldProperty.set(FieldProperty.java:44)
	at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.constructJavaBean2ndStep(Constructor.java:286)
	... 9 more
[+] Dumping Received HTTP Request. Will not be empty if PoC worked
GET /proof-of-concept HTTP/1.1
User-Agent: Java/11.0.14
Host: localhost:8000
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-alive

Further Analysis

Potential mitigations include, leveraging SnakeYaml's SafeConstructor while parsing untrusted content.

See https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in#comment-64581479 for discussion on the subject.

A fix was released in version 2.0. See https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in#comment-64876314 for more information.

Timeline

Date reported: 4/11/2022
Date fixed:
Date disclosed: 10/13/2022

Permalink: https://github.com/advisories/GHSA-mjmj-j48q-9wg2
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS1tam1qLWo0OHEtOXdnMs4AAwRm
Source: GitHub Advisory Database
Origin: Unspecified
Severity: High
Classification: General
Published: over 1 year ago
Updated: 5 months ago

CVSS Score: 8.3
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L

Identifiers: GHSA-mjmj-j48q-9wg2, CVE-2022-1471
References:

• https://github.com/google/security-research/security/advisories/GHSA-mjmj-j48q-9wg2
• https://nvd.nist.gov/vuln/detail/CVE-2022-1471
• https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in#comment-64581479
• https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in#comment-64634374
• https://bitbucket.org/snakeyaml/snakeyaml/wiki/CVE-2022-1471
• https://github.com/mbechler/marshalsec
• https://snyk.io/blog/unsafe-deserialization-snakeyaml-java-cve-2022-1471/
• https://www.github.com/mbechler/marshalsec/blob/master/marshalsec.pdf?raw=true
• https://bitbucket.org/snakeyaml/snakeyaml/commits/5014df1a36f50aca54405bb8433bc99a8847f758
• https://bitbucket.org/snakeyaml/snakeyaml/commits/acc44099f5f4af26ff86b4e4e4cc1c874e2dc5c4
• https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in#comment-64876314
• https://groups.google.com/g/kubernetes-security-announce/c/mwrakFaEdnc
• https://security.netapp.com/advisory/ntap-20230818-0015/
• http://packetstormsecurity.com/files/175095/PyTorch-Model-Server-Registration-Deserialization-Remote-Code-Execution.html
• http://www.openwall.com/lists/oss-security/2023/11/19/1
• https://github.com/advisories/GHSA-mjmj-j48q-9wg2

Repository: https://bitbucket.org/snakeyaml/snakeyaml
Blast Radius: 36.6

Affected Packages