Jackson-databind type ID cache leak (CVE-2026-91776)
CVE-2026-91776 Published on September 23, 2026
jackson-databind: unbounded growth of the type id cache in TypeDeserializerBase retains every unknown raw type ID
TypeDeserializerBase._findDeserializer() in FasterXML jackson-databind caches the resolved deserializer under the raw, attacker-supplied type ID. When name-based polymorphism is configured with a fallback, for example @JsonTypeInfo(use = Id.NAME, defaultImpl = ...), every distinct unrecognized type ID resolves to the same fallback deserializer but is retained as its own key in the _deserializers map. That map has no configurable bound and lives for the lifetime of the type deserializer, so an attacker who can repeatedly supply fresh unknown type IDs causes monotonic memory retention across requests. The reporter observed 10,000 retained entries from 10,000 distinct unknown IDs, against a single entry for a control that repeated one unknown ID the same number of times, isolating attacker-controlled key cardinality from request volume. Exploitation requires an application that enables name-based polymorphism with a defaultImpl or equivalent fallback, accepts attacker-influenced type IDs, and reuses a long-lived ObjectMapper across requests. The fix stops caching fallback resolutions for unrecognized IDs and bounds both the number of cached entries and the length of a cacheable type ID.
Vulnerability Analysis
CVE-2026-91776 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. An automatable proof of concept (POC) exploit exists. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Resource Exhaustion Vulnerability?
The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
CVE-2026-91776 has been classified to as a Resource Exhaustion vulnerability or weakness.
Products Associated with CVE-2026-91776
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Affected Versions
FasterXML jackson-databind:- Version 2.0.0, <= 2.18.10 is affected.
- Version 2.19.0, <= 2.21.6 is affected.
- Version 2.22.0, <= 2.22.2 is affected.
- Version 3.0.0, <= 3.1.6 is affected.
- Version 3.2.0, <= 3.2.2 is affected.