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High, CVSS 7.5amended

fast-xml-parser has RangeError DoS Numeric Entities Bug

CVE-2026-25128GHSA-37qj-frw5-hhjh

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (fast-xml-parser 5.3.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-25128: 0.61% estimated exploitation activity in the next 30 days; percentile 49.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary A RangeError vulnerability exists in the numeric entity processing of fast-xml-parser when parsing XML with out-of-range entity code points (e.g., � or �). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input. Details The vulnerability exists in /src/xmlparser/OrderedObjParser.js at lines 44-45: The String.fromCodePoint() method throws a RangeError when the code point exceeds the valid Unicode range (0 to 0x10FFFF / 1114111). The regex patterns can capture values far exceeding this: - [0-9]{1,7} matches up to 9,999,999 - [0-9a-fA-F]{1,6} matches up to 0xFFFFFF (16,777,215) The entity replacement in replaceEntitiesValue() (line 452) has no try-catch: This causes the RangeError to propagate uncaught, crashing the parser and any application using it. PoC Setup Create a directory with these files: package.json server.js Run Result Server crashes with: Alternative Payloads Impact Denial of Service…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-37qj-frw5-hhjh

  2. Revision 1 · created ·

    Published from osv record GHSA-37qj-frw5-hhjh

Agent brief

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# Patch Next advisory brief: CVE-2026-25128

Advisory: fast-xml-parser has RangeError DoS Numeric Entities Bug
IDs: CVE-2026-25128, GHSA-37qj-frw5-hhjh
Record: https://patchnext.com/advisories/cve-2026-25128 (revision 2, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fast-xml-parser 5.3.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fast-xml-parser: affected >= 5.0.9, <= 5.3.3; fixed in 5.3.4

## Suggested inspection (read-only)
- `npm ls fast-xml-parser --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## 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 fast-xml-parser.
- 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://osv.dev/vulnerability/GHSA-37qj-frw5-hhjh (OSV record GHSA-37qj-frw5-hhjh lists affected ranges: npm fast-xml-parser >=5.0.9 <5.3.4 (fixed))
- Verified: https://github.com/advisories/GHSA-37qj-frw5-hhjh (GitHub-reviewed advisory GHSA-37qj-frw5-hhjh lists affected ranges: npm fast-xml-parser >=5.0.9 <=5.3.3)

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