jackson-core contains core low-level incremental ("streaming") parser and generator abstractions used by Jackson Data Processor. From version 3.0.0 to before version 3.1.0, the UTF8DataInputJsonParser, which is used when parsing from a java.io.DataInput source, bypasses the maxNestingDepth constraint (default: 500) defined in StreamReadConstraints. A similar issue was found in ReaderBasedJsonParser. This allows a user to supply a JSON document with excessive nesting, which can cause a StackOverflowError when the structure is processed, leading to a Denial of Service (DoS). This issue has been patched in version 3.1.0.

jackson-databind contains the general-purpose data-binding functionality and tree-model for Jackson Data Processor. From 2.10.0 until 2.18.8, 2.21.4, and 3.1.4, jackson-databind's PolymorphicTypeValidator (PTV) is the primary safety mechanism guarding polymorphic deserialization. When polymorphic typing is enabled and a type identifier contains generic parameters (i.e. the type ID string contains <), DatabindContext.resolveAndValidateGeneric() validates only the raw container class name (the substring before <) against the configured PTV. If the container type is approved, the method parses the full canonical type string via TypeFactory.constructFromCanonical() and returns the fully parameterized type without ever validating the nested type arguments against the PTV. The nested type arguments are then resolved, instantiated, and populated as beans during deserialization. An attacker who controls the type ID can therefore place a denied class as a generic type parameter of an allowed container — for example java.util.ArrayList<com.evil.Gadget> when only java.util.ArrayList is allow-listed. The container passes the PTV check; com.evil.Gadget is loaded via Class.forName(name, true, loader), instantiated, and its properties are set from attacker-controlled JSON. This completely bypasses an explicitly configured PTV allow-list. This vulnerability is fixed in 2.18.8, 2.21.4, and 3.1.4.

Overview

A flaw in Jackson-core's JsonLocation.appendSourceDesc method allows up to 500 bytes of unintended memory content to be included in exception messages. When parsing JSON from a byte array with an offset and length, the exception message incorrectly reads from the beginning of the array instead of the logical payload start. This results in possible information disclosure in systems using pooled or reused buffers, like Netty or Vert.x.

Details

The vulnerability affects the creation of exception messages like:

JsonParseException: Unexpected character ... at [Source: (byte[])...]

When JsonFactory.createParser(byte[] data, int offset, int len) is used, and an error occurs while parsing, the exception message should include a snippet from the specified logical payload. However, the method appendSourceDesc ignores the offset, and always starts reading from index 0.

If the buffer contains residual sensitive data from a previous request, such as credentials or document contents, that data may be exposed if the exception is propagated to the client.

The issue particularly impacts server applications using:

Pooled byte buffers (e.g., Netty) Frameworks that surface parse errors in HTTP responses Default Jackson settings (i.e., INCLUDESOURCEINLOCATION is enabled)

A documented real-world example is CVE-2021-22145 in Elasticsearch, which stemmed from the same root cause.

Attack Scenario

An attacker sends malformed JSON to a service using Jackson and pooled byte buffers (e.g., Netty-based HTTP servers). If the server reuses a buffer and includes the parser’s exception in its HTTP 400 response, the attacker may receive residual data from previous requests.

Proof of Concept

java byte[] buffer = new byte[1000]; System.arraycopy("SECRET".getBytes(), 0, buffer, 0, 6); System.arraycopy("{ \"bad\": }".getBytes(), 0, buffer, 700, 10);

JsonFactory factory = new JsonFactory(); JsonParser parser = factory.createParser(buffer, 700, 20); parser.nextToken(); // throws exception

// Exception message will include "SECRET"

Patches This issue was silently fixed in jackson-core version 2.13.0, released on September 30, 2021, via PR #652.

All users should upgrade to version 2.13.0 or later.

Workarounds If upgrading is not immediately possible, applications can mitigate the issue by:

1. Disabling exception message exposure to clients — avoid returning parsing exception messages in HTTP responses. 2. Disabling source inclusion in exceptions by setting:

java jsonFactory.disable(JsonFactory.Feature.INCLUDESOURCEINLOCATION);

This prevents Jackson from embedding any source content in exception messages, avoiding leakage.

References Pull Request #652 (Fix implementation) CVE-2021-22145 (Elasticsearch exposure of this flaw)