Affected: WSO2 Identity Server, WSO2 Open Banking IAM, WSO2 Identity Server as Key Manager

A username enumeration vulnerability exists in multiple WSO2 products when Multi-Attribute Login is enabled. In this configuration, the system returns a distinct "User does not exist" error message to the login form, regardless of the validate_username setting. This behavior allows malicious actors to determine which usernames exist in the system based on observable discrepancies in the application's responses.

Exploitation of this vulnerability could aid in brute-force attacks, targeted phishing campaigns, or other social engineering techniques by confirming the validity of user identifiers within the system.

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…