jackson-core: Number Length Constraint Bypass in Async Parser Leads to Potential DoS Condition

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · 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 · score source

EPSS

• CVE-2026-18401: 0.41% estimated exploitation activity in the next 30 days; percentile 35.12 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The non-blocking (async) JSON parser in jackson-core bypasses the maxNumberLength constraint (default: 1000 characters) defined in StreamReadConstraints. This allows an attacker to send JSON with arbitrarily long numbers through the async parser API, leading to excessive memory allocation and potential CPU exhaustion, resulting in a Denial of Service (DoS). The standard synchronous parser correctly enforces this limit, but the async parser fails to do so, creating an inconsistent enforcement policy. Details The root cause is that the async parsing path in NonBlockingUtf8JsonParserBase (and related classes) does not call the methods responsible for number length validation. - The number parsing methods (e.g., finishNumberIntegralPart) accumulate digits into the TextBuffer without any length checks. - After parsing, they call valueComplete(), which finalizes the token but does not call resetInt() or resetFloat(). - The resetInt()/resetFloat() methods in ParserBase are where the…

Published by the source

28 Feb 2026, 02:01 UTC

Last modified by the source

1 Sep 2026, 18:57 UTC

Source last checked

26 Oct 2026, 16:55 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-72hv-8253-57qq

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# Patch Next advisory brief: CVE-2026-18401

Advisory: jackson-core: Number Length Constraint Bypass in Async Parser Leads to Potential DoS Condition
IDs: CVE-2026-18401, GHSA-72hv-8253-57qq
Record: https://patchnext.com/advisories/cve-2026-18401 (revision 1, source checked 26 Oct 2026, 16:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: com.fasterxml.jackson.core:jackson-core 2.21.1, 2.18.6; tools.jackson.core:jackson-core 3.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.fasterxml.jackson.core:jackson-core: affected >= 2.19.0, < 2.21.1; >= 2.15.0, <= 2.18.5; fixed in 2.18.6, 2.21.1
- Maven tools.jackson.core:jackson-core: affected >= 3.0.0, < 3.1.0; fixed in 3.1.0

## Suggested inspection (read-only)
- Maven com.fasterxml.jackson.core:jackson-core: check the installed version with your package manager.
- Maven tools.jackson.core:jackson-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.fasterxml.jackson.core:jackson-core, tools.jackson.core:jackson-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-72hv-8253-57qq (GitHub-reviewed advisory GHSA-72hv-8253-57qq lists affected ranges: Maven tools.jackson.core:jackson-core >=3.0.0 =2.19.0 =2.15.0 <=2.18.5)

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