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CVE-2026-18401— jackson-core: Number length constraint bypass in non-blocking (async) JSON parser leads to potential denial of service

Quick assessment

Affected
FasterXML jackson-core
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

FasterXML Jackson-core是FasterXML组织开源的一个JSON处理库。 FasterXML Jackson-core 2.15.0至2.18.5版本、2.19.0至2.21.0版本和3.0.0至3.0.x版本存在资源管理错误漏洞，该漏洞源于非阻塞（异步）JSON解析器未强制执行StreamReadConstraints中定义的maxNumberLength约束，可能导致攻击者提交任意长度数字令牌，造成过度内存分配和CPU耗尽，导致拒绝服务。

CVSS 6.9 · Medium EPSS 0.41% · P33

Affected Version Matrix 6

VendorProduct Version RangeStatus
FasterXML jackson-core 2.15.0≤ 2.18.5 affected
2.18.6 unaffected
2.19.0< 2.21.1 affected
2.21.1 unaffected
3.0.0< 3.1.0 affected
3.1.0 unaffected
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I. Basic Information for CVE-2026-18401

Vulnerability Information
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Vulnerability Title
jackson-core: Number length constraint bypass in non-blocking (async) JSON parser leads to potential denial of service
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5
Vulnerability Title
FasterXML Jackson-core 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
FasterXML Jackson-core是FasterXML组织开源的一个JSON处理库。 FasterXML Jackson-core 2.15.0至2.18.5版本、2.19.0至2.21.0版本和3.0.0至3.0.x版本存在资源管理错误漏洞，该漏洞源于非阻塞（异步）JSON解析器未强制执行StreamReadConstraints中定义的maxNumberLength约束，可能导致攻击者提交任意长度数字令牌，造成过度内存分配和CPU耗尽，导致拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
FasterXML jackson-core 2.15.0 ~ 2.18.5 -
FasterXML jackson-core 3.0.0 ~ 3.1.0 -

II. Public POCs for CVE-2026-18401

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III. Intelligence Information for CVE-2026-18401

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Patches & Fixes for CVE-2026-18401 (2)

Vendor Advisories for CVE-2026-18401 (1)

IV. Related Vulnerabilities

Same product: jackson-core
Same vendor: FasterXML
Same weakness: CWE-770

V. Comments for CVE-2026-18401

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