Jackson Databind Forward-Reference Deserialization DoS
CVE-2026-91777 Published on September 23, 2026
jackson-databind: quadratic forward-reference completion in Collection and Map deserializers
Forward-reference completion for @JsonIdentityInfo object IDs in FasterXML jackson-databind performs a linear scan of the pending-reference accumulator for every resolved ID. The affected paths are CollectionDeserializer.CollectionReferringAccumulator.resolveForwardReference() and the equivalent implementation in MapDeserializer. When a document first creates N unresolved object-ID references in an identity-enabled collection or map and then defines those same IDs in reverse order, completion performs on the order of N * (N + 1) / 2 identity comparisons, so a shallow document whose size grows linearly causes quadratic CPU work during deserialization. The reporter instrumented equals() calls on the ID class and measured exactly 2,003,000 comparisons at N = 2,000, against zero comparisons in the pending-reference lookup path for an equally sized control in which every reference was already resolved. The input requires no deep nesting and no syntactically unusual JSON. Exploitation requires an application that deserializes attacker-influenced JSON into an identity-enabled collection or map. The fix replaces the repeated linear lookup with a keyed pending-reference structure.
Vulnerability Analysis
CVE-2026-91777 can be exploited 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-2026-91777 has been classified to as a Resource Exhaustion vulnerability or weakness.
Products Associated with CVE-2026-91777
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Affected Versions
FasterXML jackson-databind:- Version 2.5.0, <= 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.