--- id: "CVE-2026-110879" kind: "vulnerability" aliases: ["CVE-2026-110879"] title: "jackson-databind: generic type IDs bypass class validation, enabling remote code execution" severity: "critical" cvss: 9.8 epss: null exploited: false status: "open" category: "package" products: [] ecosystems: [] tags: ["jackson", "java", "package", "self-hosted", "spring"] not_affected_if: ["default-config", "no-polymorphic-deserialization"] published_at: "2026-10-28T01:16:55+00:00" first_seen_at: "2026-10-28T01:30:10+00:00" updated_at: "2026-10-28T01:31:41+00:00" sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110879", "first_seen_at": "2026-10-28T01:30:10+00:00"}] --- # jackson-databind: generic type IDs bypass class validation, enabling remote code execution Jackson's class-name type validation checks the outer class of a generic type ID but not the classes passed as its generic arguments. An attacker who controls JSON input can make the server deserialize a gadget class, and with Spring on the classpath and attacker-controlled XML this reaches ProcessBuilder.start() and arbitrary command execution. _Summary, check and fix written by a model from the sources; labelled as such._ ## How to check - Find the jackson-databind version in the build file or lockfile, for example with `mvn dependency:tree | grep jackson-databind` or `gradle dependencies | grep jackson-databind` - Check whether the application enables default typing or uses `@JsonTypeInfo(use = Id.CLASS)` on deserialized types - Check whether Spring is on the classpath ## Fix - Upgrade com.fasterxml.jackson.core:jackson-databind to a release that contains the fix for this issue (the fixed version is unknown from the sources) - Upgrade tools.jackson.core:jackson-databind to a fixed 3.x release (unknown from the sources) - Disable class-name default typing where it is not needed ## Timeline - 2026-10-28T01:30:10+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-110879 ## From the sources jackson-databind validates the outer class of a class-name type ID but accepts attacker-selected classes inside its generic arguments, even when those classes violate the declared type or would be rejected as direct type IDs. This bypasses the generic-argument validation added for CVE-2026-54512 (GHSA-j3rv-43j4-c7qm), of which this is an incomplete fix. DatabindContext._resolveAndValidateGeneric() checks the outer class against the declared base type and then passes each argument from the type ID to _validateTypeParameter(), which validates the argument against the outer base type rather than enforcing its corresponding declared generic binding. It also invokes validators with arguments that have not passed the subtype check those validators expect. Under the default DefaultBaseTypeLimitingValidator this accepts an unrelated class inside a generic subtype even when the same class is rejected as a direct type ID. Where an allowIfBaseType(...) rule approves the outer type, Jackson substitutes LaissezFaireSubTypeValidator, so the configured validator no longer restricts the embedded arguments. The element type of a plain array type ID such as [Lpkg.Gadget; is likewise left unvalidated once the array's base type is approved. Affected paths include annotation-based class-name polymorphism with a default Jackson 3.x JsonMapper, configured default typing in both Jackson 2.x and 3.x, and integrations that expose that default typing. The default-validator case requires no application-authored validator: with @JsonTypeInfo(use = Id.CLASS), a direct gadget type ID is rejected as "Not a subtype", while a type ID naming a generic wrapper around the same gadget is accepted and deserialized, including attacker-supplied bean properties. Where class-name default typing permits Map, a property declared as Map accepts HashMap; map-key discovery then passes the attacker-controlled JSON property name to the selected class's one-string constructor. With Spring on the classpath and attacker-controlled XML the application can load, that constructor loads the XML and invokes ProcessBuilder.start() under the application account, giving arbitrary command execution. This issue affects com.fasterxml.jackson.core:jackson-databind from 2.10.0 and tools.jackson.core:jackson-databind from 3.0.0. Releases before 2.10.0 are not affected, because PolymorphicTypeValidator was introduced in jackson-databind 2.10.0. --- _Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_