Summary
SnakeYaml Constructor Deserialization Remote Code Execution
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.
Timeline
Date reported: 4/11/2022
Date fixed: 30/12/2022
Date disclosed: 10/13/2022
Impact
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2022-1471 has a CVSS score of 8.3 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2022-1471? CVE-2022-1471 is a high-severity improper input validation vulnerability in org.yaml:snakeyaml (maven), affecting versions <= 1.33. It is fixed in 2.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2022-1471? CVE-2022-1471 has a CVSS score of 8.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.yaml:snakeyaml are affected by CVE-2022-1471? org.yaml:snakeyaml (maven) versions <= 1.33 is affected.
- Is there a fix for CVE-2022-1471? Yes. CVE-2022-1471 is fixed in 2.0. Upgrade to this version or later.
- Is CVE-2022-1471 exploitable, and should I be worried? Whether CVE-2022-1471 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2022-1471 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2022-1471? Upgrade
org.yaml:snakeyamlto 2.0 or later.