Affected: Ubuntu:Pro:14.04:LTS: jackson-databind, Ubuntu:Pro:16.04:LTS: jackson-databind, Ubuntu:18.04:LTS: jackson-databind, Ubuntu:20.04:LTS: jackson-databind, Ubuntu:22.04:LTS: jackson-databind, Ubuntu:24.04:LTS: jackson-databind, Ubuntu:26.10: jackson-databind, Ubuntu:26.04:LTS: jackson-databind

jackson-databind validates the outer class of a class-name type ID but accepts attacker-selected classes inside its generic arguments, even when those classes violate the declared type or would be rejected as direct type IDs. This bypasses the generic-argument validation added for CVE-2026-54512 (GHSA-j3rv-43j4-c7qm), of which this is an incomplete fix. DatabindContext._resolveAndValidateGeneric() checks the outer class against the declared base type and then passes each argument from the type ID to _validateTypeParameter(), which validates the argument against the outer base type rather than enforcing its corresponding declared generic binding. It also invokes validators with arguments that have not passed the subtype check those validators expect. Under the default DefaultBaseTypeLimitingValidator this accepts an unrelated class inside a generic subtype even when the same class is rejected as a direct type ID. Where an allowIfBaseType(...) rule approves the outer type, Jackson substitutes LaissezFaireSubTypeValidator, so the configured validator no longer restricts the embedded arguments. The element type of a plain array type ID such as [Lpkg.Gadget; is likewise left unvalidated once the array's base type is approved. Affected paths include annotation-based class-name polymorphism with a default Jackson 3.x JsonMapper, configured default typing in both Jackson 2.x and 3.x, and integrations that expose that default typing. The default-validator case requires no application…