Affected: FasterXML jackson-core
The non-blocking (asynchronous) JSON parser in jackson-core does not enforce the maxNumberLength constraint defined in StreamReadConstraints (default: 1000 characters). An attacker able to submit JSON to an application that uses the async parser API can supply a number token of arbitrary length, leading to excessive memory allocation and potential CPU exhaustion, resulting in a denial of service.
The synchronous parser enforces this limit correctly, so the constraint is applied inconsistently depending on which parsing API the application uses.
Root cause: the async parsing path in NonBlockingUtf8JsonParserBase and related classes never invokes the number length validation methods. Number parsing methods such as _finishNumberIntegralPart() accumulate digits into the TextBuffer without any length check, then call _valueComplete() to finalize the token. _valueComplete() does not call resetInt() or resetFloat(), which are the methods in ParserBase where validateIntegerLength() and validateFPLength() are performed. Because that validation step is skipped, maxNumberLength is never enforced on the async code path.
Impact: an attacker sending a JSON document containing an arbitrarily long number to an application using the async parser (for example a Spring WebFlux or other reactive application) can cause unbounded allocation in the TextBuffer and an OutOfMemoryError. If the application subsequently calls getBigIntegerValue() or getDecimalValue(), the JVM may additionally…
Affected: Maven: com.fasterxml.jackson.core:jackson-core, Maven: tools.jackson.core:jackson-core
## Summary
The fix released in jackson-core `2.18.6` and `2.21.1` for [GHSA-72hv-8253-57qq](https://github.com/FasterXML/jackson-core/security/advisories/GHSA-72hv-8253-57qq) (Number Length Constraint Bypass in Async Parser, published 2026-02-28) is incomplete. The fix commit `b0c428e6` (#1555) wired `validateIntegerLength` into a new `_setIntLength` helper and called it at every place where the integer portion of a number is *decided* (terminator byte arrived, `.` / `e/E` seen, end-of-feed inside a fully-buffered value). It did not call it on the much more attacker-relevant path: "ran out of input while still inside `MINOR_NUMBER_INTEGER_DIGITS`, return `NOT_AVAILABLE` to caller".
As a result, an attacker who streams JSON to a non-blocking parser in many small chunks, without ever sending a terminator byte, can keep the parser inside `MINOR_NUMBER_INTEGER_DIGITS` indefinitely. `_textBuffer.expandCurrentSegment()` grows on every chunk, and `validateIntegerLength` is never invoked. The accumulator is only gated by `maxStringLength` (20 MiB default) — a **~20,000x amplification** of the documented `maxNumberLength` (1000 default).
This is the same vulnerability class, same advisory wording ("Memory Exhaustion: Unbounded allocation in TextBuffer from excessively long numbers"), same parser class — just the streaming path the original fix didn't cover. The fix to the *fraction* path is correct (see `_finishFloatFraction` at line 1834-1837 of `NonBlockingUtf8JsonParserBase.jav…