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Resolve vulnerability: Java Unsafe Jackson Deserialization

Igor Drozdovrequested to merge
remediate/java-unsafe-jackson-deserialization-D20250416T084239 into main

MR created from vulnerability: Java Unsafe Jackson Deserialization

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Description:

Jackson deserialization vulnerability in Java arises when applications using the Jackson library deserialize untrusted JSON data without proper safeguards, potentially leading to severe security risks like remote code execution (RCE).

  1. Avoid using polymorphic type handling and avoid deserializing user input.
  2. Absolutely avoid using Unsafe Base Types for fields. Types considered unsafe base types include:
  • java.lang.Object
  • java.io.Closeable
  • java.io.Serializable
  • java.lang.AutoCloseable
  • java.lang.Cloneable
  • java.util.logging.Handler
  • javax.naming.Referenceable
  • javax.sql.DataSource
    List of types compiled from a set of all known deserialization "gadgets", types they implement. Reference : https://github.com/FasterXML/jackson-databind/issues/2587
  1. For explicit per-type/per-property polymorphic handling (@JsonTypeInfo), don’t use:
  • @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS) annotation 
  • @JsonTypeInfo(use = JsonTypeInfo.Id.MINIMAL_CLASS) annotation Instead use:
  • @JsonTypeInfo(use = JsonTypeInfo.Id.NAME) annotation where possible.
  1. Use Safe Default Typing feature properly. Don’t use the deprecated ‘enableDefaultTyping()’.
  1. Avoid using com.fasterxml.jackson.databind.jsontype.impl.LaissezFaireSubTypeValidator
  1. Use MapperFeature.BLOCK_UNSAFE_POLYMORPHIC_BASE_TYPES where possible.
  1. Regularly update to the latest version of Jackson library.

Analysis:

The reported vulnerability is related to unsafe Jackson deserialization (CWE-502: Deserialization of Untrusted Data). The specific issue is in the ObjectMapperNoncompliant method where enableDefaultTyping() is called on the Jackson ObjectMapper.

The vulnerability occurs because enabling default typing allows Jackson to deserialize arbitrary Java types, including those that could be malicious. This creates a potential remote code execution vulnerability where an attacker could craft malicious JSON input that, when deserialized, could execute arbitrary code on the system.

Key concerns:

  1. enableDefaultTyping() is deprecated since Jackson 2.10 due to security concerns
  2. Allowing polymorphic deserialization of untrusted input is dangerous
  3. The code is processing input from a File object, which could contain malicious content

The code already shows a compliant version that uses deactivateDefaultTyping(), but this is not the best modern approach to handle this security concern.

Summary:

  1. Vulnerability: The code uses Jackson's enableDefaultTyping() method, which is deprecated and creates a remote code execution vulnerability through unsafe deserialization of untrusted data (CWE-502).

  2. Fix Explanation: The fix implements the following security improvements:

    • Replaces the deprecated and unsafe enableDefaultTyping() with the newer activateDefaultTyping() method
    • Uses a PolymorphicTypeValidator to control which types can be deserialized
    • Sets the default typing to NONE to restrict polymorphic deserialization

  3. Security Impact: The new implementation:

    • Prevents arbitrary class deserialization
    • Maintains type safety during deserialization
    • Reduces the risk of remote code execution attacks
// Before - Vulnerable
mapper.enableDefaultTyping();

// After - Secure
mapper.activateDefaultTyping(mapper.getPolymorphicTypeValidator(), 
    ObjectMapper.DefaultTyping.NONE);

For additional security, consider:

  • Implementing a custom PolymorphicTypeValidator to whitelist allowed classes
  • Using specific type information instead of generic List.class
  • Validating input before deserialization
  • Implementing proper error handling for malformed input

Identifiers:

  • CWE-502
  • java_deserialization_rule-JacksonUnsafeDeserialization

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