CVE-2026-18401

A flaw was found in jackson-core. The non-blocking (asynchronous) JSON parser does not properly enforce the maximum number length constraint. A remote attacker can exploit this by submitting a specially crafted JSON document containing an arbitrarily long number to an application using the asynchronous parser. This can lead to excessive memory allocation and CPU exhaustion, resulting in a denial of service (DoS) for the affected application.

Red Hat's assessment of this vulnerability differs from the reported vendor severity. The flaw exists only in jackson-core's non-blocking (asynchronous) JSON parser, which does not enforce the maxNumberLength constraint defined by StreamReadConstraints. Applications that use the standard, synchronous parsing API (the default for the vast majority of Java applications using jackson-core, including via ObjectMapper) enforce this limit correctly and are not affected by this specific code path. Only applications that explicitly invoke the non-blocking parser API, typically reactive frameworks processing untrusted network input, are exposed to the described memory/CPU exhaustion behavior. Red Hat rates this issue as Moderate.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

No mitigation is available for applications that use the non-blocking/async parser API with untrusted input. Affected users should upgrade to jackson-core 2.18.6, 2.21.1, 3.1.0, or later. Applications that only use the standard (synchronous) parser API are not affected and require no action.