[MAVEN:GHSA-MJMJ-J48Q-9WG2] 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
Package | Affected Version |
---|---|
pkg:maven/org.yaml/snakeyaml | <= 1.33 |
Package | Fixed Version |
---|---|
pkg:maven/org.yaml/snakeyaml | = 2.0 |
- ID
- MAVEN:GHSA-MJMJ-J48Q-9WG2
- Severity
- high
- URL
- https://github.com/advisories/GHSA-mjmj-j48q-9wg2
- Published
-
2022-12-12T21:19:47
(21 months ago) - Modified
-
2023-11-20T22:16:15
(10 months ago) - Rights
- Maven Security Team
- Other Advisories
# CVE | Description | CVSS | EPSS | EPSS Trend (30 days) | Affected Products | Weaknesses | Security Advisories | Exploits | PoC | Pubblication Date | Modification Date |
---|---|---|---|---|---|---|---|---|---|---|---|
# CVE | Description | CVSS | EPSS | EPSS Trend (30 days) | Affected Products | Weaknesses | Security Advisories | PoC | Pubblication Date | Modification Date |