Summary In BeanDeserializerBase.createContextual(), per-property @JsonIgnoreProperties exclusions are applied by handleByNameInclusion(), producing a contextual deserializer whose BeanPropertyMap has the ignored properties removed. The subsequent per-property case-insensitivity block (triggered by @JsonFormat(ACCEPTCASEINSENSITIVEPROPERTIES)) rebuilds from this.beanProperties (the original, unfiltered map) instead of contextual.beanProperties, then overwrites the filtered map — restoring every property handleByNameInclusion had just removed. The ignored property becomes writable again.

Impact An application that both enables case-insensitive matching and relies on per-property @JsonIgnoreProperties to keep a field unwritable can have that field set from untrusted JSON (mass-assignment-style write).

Affected / Patched Fixed in 2.18.9, 2.21.5 and 3.1.4.

Severity / CWE Maintainer: minor. Reporter: Moderate. CWE-915.

Upstream fix FasterXML/jackson-databind#5962 (PR #5964, 0e1b0b2), milestone 3.1.4. Released 2026-06-04.

Credits Omkhar Arasaratnam (@omkhar) - finder.