CVE-2026-18401
jackson-core: Number length constraint bypass in non-blocking (async) JSON parser leads to potential denial of service
Description
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 be tied up in O(n^2) BigInteger parsing, causing CPU-based denial of service. No privileges or user interaction beyond the ability to submit data for parsing are required. This issue affects com.fasterxml.jackson.core:jackson-core from version 2.15.0 through 2.18.5 and from 2.19.0 through 2.21.0, and tools.jackson.core:jackson-core from 3.0.0 through 3.0.x. Versions prior to 2.15.0 are not affected, because StreamReadConstraints -- which defines the maxNumberLength setting -- was first introduced in jackson-core 2.15.0, so no such constraint exists to be bypassed in earlier releases. Note that GHSA-72hv-8253-57qq records the lower bound of the affected 2.x range as 2.0.0.
INFO
Published Date :
Aug. 4, 2026, 3:16 p.m.
Last Modified :
Oct. 23, 2026, 11:10 p.m.
Remotely Exploit :
Yes !
Source :
36c7be3b-2937-45df-85ea-ca7133ea542c
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | MEDIUM | 36c7be3b-2937-45df-85ea-ca7133ea542c | ||||
| CVSS 4.0 | MEDIUM | 36c7be3b-2937-45df-85ea-ca7133ea542c |
Solution
- Update jackson-core to a fixed version.
- Verify asynchronous parsing validates number length.
- Consider synchronous parsing if updates are unavailable.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-18401.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-18401 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-18401
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-18401 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-18401 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Translated by [email protected]
Oct. 23, 2026
Action Type Old Value New Value Added Translation Title: jackson-core de FasterXML, Description: El analizador JSON no bloqueante (asíncrono) en jackson-core no aplica la restricción maxNumberLength definida en StreamReadConstraints (predeterminado: 1000 caracteres). Un atacante capaz de enviar JSON a una aplicación que utiliza la API del analizador asíncrono puede proporcionar un token numérico de longitud arbitraria, lo que lleva a una asignación excesiva de memoria y un posible agotamiento de la CPU, resultando en una denegación de servicio. El analizador síncrono aplica este límite correctamente, por lo que la restricción se aplica de forma inconsistente dependiendo de qué API de análisis utilice la aplicación. Causa raíz: la ruta de análisis asíncrono en NonBlockingUtf8JsonParserBase y clases relacionadas nunca invoca los métodos de validación de longitud de números. Los métodos de análisis de números como _finishNumberIntegralPart() acumulan dígitos en el TextBuffer sin ninguna verificación de longitud, luego llaman a _valueComplete() para finalizar el token. _valueComplete() no llama a resetInt() ni a resetFloat(), que son los métodos en ParserBase donde se realizan validateIntegerLength() y validateFPLength(). Debido a que ese paso de validación se omite, maxNumberLength nunca se aplica en la ruta de código asíncrono. Impacto: un atacante que envía un documento JSON que contiene un número arbitrariamente largo a una aplicación que utiliza el analizador asíncrono (por ejemplo, una aplicación Spring WebFlux u otra aplicación reactiva) puede causar una asignación ilimitada en el TextBuffer y un OutOfMemoryError. Si la aplicación posteriormente llama a getBigIntegerValue() o getDecimalValue(), la JVM puede además quedar ocupada en el análisis de BigInteger en O(n^2), causando una denegación de servicio basada en CPU. No se requieren privilegios ni interacción del usuario más allá de la capacidad de enviar datos para su análisis. Este problema afecta a com.fasterxml.jackson.core:jackson-core desde la versión 2.15.0 hasta la 2.18.5 y desde la 2.19.0 hasta la 2.21.0, y a tools.jackson.core:jackson-core desde la 3.0.0 hasta la 3.0.x. Las versiones anteriores a la 2.15.0 no se ven afectadas, porque StreamReadConstraints -- que define la configuración maxNumberLength -- se introdujo por primera vez en jackson-core 2.15.0, por lo que no existe tal restricción que pueda ser eludida en versiones anteriores. Tenga en cuenta que GHSA-72hv-8253-57qq registra el límite inferior del rango 2.x afectado como 2.0.0. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 04, 2026
Action Type Old Value New Value Added Reference https://github.com/FasterXML/jackson-core/security/advisories/GHSA-72hv-8253-57qq Added SSVC {'id': 'CVE-2026-18401', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-04T17:58:30.797291Z'} -
New CVE Received by 36c7be3b-2937-45df-85ea-ca7133ea542c
Aug. 04, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://github.com/FasterXML/jackson-core', 'vendor': 'FasterXML', 'product': 'jackson-core', 'versions': [{'status': 'affected', 'version': '2.15.0', 'versionType': 'maven', 'lessThanOrEqual': '2.18.5'}, {'status': 'unaffected', 'version': '2.18.6', 'versionType': 'maven'}, {'status': 'affected', 'version': '2.19.0', 'lessThan': '2.21.1', 'versionType': 'maven'}, {'status': 'unaffected', 'version': '2.21.1', 'versionType': 'maven'}], 'packageName': 'com.fasterxml.jackson.core:jackson-core', 'programFiles': ['src/main/java/com/fasterxml/jackson/core/json/async/NonBlockingUtf8JsonParserBase.java'], 'collectionURL': 'https://repo.maven.apache.org/maven2', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'NonBlockingUtf8JsonParserBase._finishNumberIntegralPart'}, {'name': 'NonBlockingUtf8JsonParserBase._valueComplete'}]}, {'repo': 'https://github.com/FasterXML/jackson-core', 'vendor': 'FasterXML', 'product': 'jackson-core', 'versions': [{'status': 'affected', 'version': '3.0.0', 'lessThan': '3.1.0', 'versionType': 'maven'}, {'status': 'unaffected', 'version': '3.1.0', 'versionType': 'maven'}], 'packageName': 'tools.jackson.core:jackson-core', 'programFiles': ['src/main/java/tools/jackson/core/json/async/NonBlockingUtf8JsonParserBase.java'], 'collectionURL': 'https://repo.maven.apache.org/maven2', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'NonBlockingUtf8JsonParserBase._finishNumberIntegralPart'}, {'name': 'NonBlockingUtf8JsonParserBase._valueComplete'}]}] Added Description 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 be tied up in O(n^2) BigInteger parsing, causing CPU-based denial of service. No privileges or user interaction beyond the ability to submit data for parsing are required. This issue affects com.fasterxml.jackson.core:jackson-core from version 2.15.0 through 2.18.5 and from 2.19.0 through 2.21.0, and tools.jackson.core:jackson-core from 3.0.0 through 3.0.x. Versions prior to 2.15.0 are not affected, because StreamReadConstraints -- which defines the maxNumberLength setting -- was first introduced in jackson-core 2.15.0, so no such constraint exists to be bypassed in earlier releases. Note that GHSA-72hv-8253-57qq records the lower bound of the affected 2.x range as 2.0.0. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-770 Added Reference https://github.com/FasterXML/jackson-core/commit/b0c428e6f993e1b5ece5c1c3cb2523e887cd52cf Added Reference https://github.com/FasterXML/jackson-core/pull/1555 Added Reference https://github.com/FasterXML/jackson-core/security/advisories/GHSA-72hv-8253-57qq