CVE-2026-83557

Summary

DefaultBaseTypeLimitingValidator is the PolymorphicTypeValidator applied automatically whenever @JsonTypeInfo is used without an explicitly configured custom validator. It denies polymorphic resolution only for a fixed set of "unsafe base types", and its isSafeSubType method returns true unconditionally for every base type outside that set. java.lang.Comparable was absent from the list despite being implemented by a very large fraction of JDK and application classes, comparable in breadth to java.io.Serializable, which is on the list for that reason. An application declaring an @JsonTypeInfo-annotated property or class with Comparable as its base type, and no custom PolymorphicTypeValidator, will accept a type identifier for essentially any class implementing Comparable. This yields an attacker-controlled object instantiation primitive; a demonstrated case constructs a java.io.File for an arbitrary attacker-chosen path, which becomes path-traversal-adjacent if the application subsequently calls path-sensitive methods on the value. No class implementing Comparable has been identified that yields code execution through deserialization alone. Global Default Typing via activateDefaultTyping is not affected, because that method structurally requires an explicit PolymorphicTypeValidator argument. This affects com.fasterxml.jackson.core:jackson-databind from 2.11.0 before 2.18.10, from 2.19.0 before 2.21.6, and from 2.22.0 before 2.22.2, and tools.jackson.core:jackson-databind from 3.0.0 before 3.1.6 and from 3.2.0 before 3.2.2. Users should upgrade to 2.18.10, 2.21.6, 2.22.2, 3.1.6, or 3.2.2.

Affected Software

Weaknesses

• CWE-502: CWE-502 Deserialization of Untrusted Data
• CWE-915: CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes

Workarounds

Configure an explicit restrictive PolymorphicTypeValidator rather than relying on the default validator, or avoid declaring java.lang.Comparable as the base type of an @JsonTypeInfo-annotated property or class. Narrowing the declared base type to an application-specific interface also removes the exposure.

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-gx83-3vf8-gh7j

References

• https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-gx83-3vf8-gh7j
• https://github.com/FasterXML/jackson-databind/pull/6155
• https://github.com/FasterXML/jackson-databind/issues/6156
• https://github.com/FasterXML/jackson-databind/commit/eb3b7fc0f9c0d27f471550ac3316b17d1987388f

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