Using unsafe Jackson deserialization configuration is security-sensitive. It has led in the past to the following vulnerabilities:

- CVE-2017-4995
- CVE-2018-19362

When Jackson is configured to allow Polymorphic Type Handling (aka PTH), formerly known as Polymorphic Deserialization, "deserialization gadgets" may allow an attacker to perform remote code execution.

This rule raises an issue when:

- `enableDefaultTyping()` is called on an instance of `com.fasterxml.jackson.databind.ObjectMapper` or `org.codehaus.jackson.map.ObjectMapper`.
- or when the annotation `@JsonTypeInfo` is set at class, interface or field levels and configured with `use = JsonTypeInfo.Id.CLASS` or `use = Id.MINIMAL_CLASS`.

## Ask Yourself Whether

- You configured the Jackson deserializer as mentioned above.
- The serialized data might come from an untrusted source.

There is a risk if you answered yes to any of those questions.

## Recommended Secure Coding Practices

- Use the latest patch versions of `jackson-databind` blocking the already discovered "deserialization gadgets".
- Avoid using the default typing configuration: `ObjectMapper.enableDefaultTyping()`.
- If possible, use `@JsonTypeInfo(use = Id.NAME)` instead of `@JsonTypeInfo(use = Id.CLASS)` or `@JsonTypeInfo(use = Id. MINIMAL_CLASS)` and so rely on `@JsonTypeName` and `@JsonSubTypes`.

## Sensitive Code Example

    ObjectMapper mapper = new ObjectMapper();
    mapper.enableDefaultTyping(); // Sensitive

    @JsonTypeInfo(use = Id.CLASS) // Sensitive
    abstract class PhoneNumber {
    }

## See

- OWASP - Top 10 2021 Category A8 - Software and Data Integrity Failures
- OWASP - Top 10 2017 Category A8 - Insecure Deserialization
- OWASP - Deserialization of untrusted data
- CWE - CWE-502 - Deserialization of Untrusted Data
- On Jackson CVEs: Don’t Panic
- CVE-2017-1509
- CVE-2017-7525
- Derived from FindSecBugs rule JACKSON_UNSAFE_DESERIALIZATION