CVE-2026-54512 — jackson-databind: PolymorphicTypeValidator bypass via generic type parameters allows arbitrary class instantiation

Affected: FasterXML jackson-databind

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, jackson-databind's PolymorphicTypeValidator (PTV) is the primary safety mechanism guarding polymorphic deserialization. When polymorphic typing is enabled and a type identifier contains generic parameters (i.e. the type ID string contains <), DatabindContext._resolveAndValidateGeneric() validates only the raw container class name (the substring before <) against the configured PTV. If the container type is approved, the method parses the full canonical type string via TypeFactory.constructFromCanonical() and returns the fully parameterized type without ever validating the nested type arguments against the PTV. The nested type arguments are then resolved, instantiated, and populated as beans during deserialization. An attacker who controls the type ID can therefore place a denied class as a generic type parameter of an allowed container — for example java.util.ArrayList<com.evil.Gadget> when only java.util.ArrayList is allow-listed. The container passes the PTV check; com.evil.Gadget is loaded via Class.forName(name, true, loader), instantiated, and its properties are set from attacker-controlled JSON. This completely bypasses an explicitly configured PTV allow-list. This vulnerability is fixed in 2.18.8, 2.21.4, and 3.1.4.

GHSA-5hh8-q8hv-fr38 — jackson-databind has @JsonView bypass for setterless creator properties

Affected: Maven: com.fasterxml.jackson.core:jackson-databind, Maven: tools.jackson.core:jackson-databind

## Summary In `BeanDeserializer._deserializeUsingPropertyBased`, the active-view (`@JsonView`) filter was applied only to creator properties; the regular property-buffering branch performed no `prop.visibleInView(activeView)` check. A change making `SetterlessProperty.isMerging()` return `true` routed setterless Collection/Map properties through this unguarded path, so a setterless collection annotated with a restricted `@JsonView` is populated from attacker JSON even when the active view excludes it.

## Impact View-restricted (e.g. admin-only) setterless collection/map properties can be written from untrusted JSON despite `@JsonView` gating — an access-control / mass-assignment bypass. No RCE or DoS.

## Affected / Patched (verified via `git tag --contains`) - 2.21 line: `>= 2.21.0, < 2.21.4` -> fixed in **2.21.4** (backport `94c5d21`, #5970) - 3.x line: `>= 3.0.0, < 3.1.4` -> fixed in **3.1.4** (#5969, `5bf23ed`)

## Severity / CWE Maintainer: minor. Reporter: HIGH. CWE-863 (Incorrect Authorization); related CWE-1220.

## Credits Omkhar Arasaratnam (@omkhar) - finder.

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CVE-2026-54512 — jackson-databind: PolymorphicTypeValidator bypass via generic type parameters allows arbitrary class instantiation

GHSA-5hh8-q8hv-fr38 — jackson-databind has @JsonView bypass for setterless creator properties