CVE-2026-91776: jackson-databind Denial of Service (CVSS 7.5)

Description

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.45%

36.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
FasterXML	jackson-databind	>= 2.0.0, <= 2.18.10; >= 2.19.0, <= 2.21.6; >= 2.22.0, <= 2.22.2
FasterXML	jackson-databind	>= 3.0.0, <= 3.1.6; >= 3.2.0, <= 3.2.2

References

Timeline

Published: Sep 23, 2026
Last Modified: Sep 24, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-91776?

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.

How severe is CVE-2026-91776?

CVE-2026-91776 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.45% probability of exploitation in the next 30 days.

How do I fix CVE-2026-91776?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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