Jackson-core Vulnerable to Memory Disclosure via Source Snippet in JsonLocation

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., INCLUDE_SOURCE_IN_LOCATION 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

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.INCLUDE_SOURCE_IN_LOCATION);

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)