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High, CVSS 8.7amended

xmldom: Creation-time XML Name/QName validation is bypassable via an embedded line terminator, allowing injection on the default serialization path

CVE-2026-83609GHSA-3px3-54cx-rmw9

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@xmldom/xmldom 0.9.12), 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 4.0
8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-83609: 0.54% estimated exploitation activity in the next 30 days; percentile 45.65 (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 An embedded line terminator bypasses xmldom's always-on, WHATWG-mandated creation-time name validation. createElementNS, createAttributeNS, createDocumentType, and createAttribute should reject a malformed qualified name with InvalidCharacterError, but a name whose first line is well-formed slips through and enters the DOM. On serialization it is emitted verbatim, so the characters after the line terminator inject markup into the output. The injection reaches the default serialization path, and enabling requireWellFormed does not prevent it. Details createElementNS, createAttributeNS, and createDocumentType route through validateQualifiedName, and createAttribute performs the analogous check; each validates the name with g.QNameexact.test(name). QNameexact = reg('^', QName, '$') inherits the m flag from xmldom's shared regexp builder, so the matcher accepts any name whose first line is a valid QName and leaves the remaining lines unconstrained (see Root Cause). Root Cause 1.…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-3px3-54cx-rmw9

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-3px3-54cx-rmw9

  4. Revision 1 · created ·

    Published from ghsa record GHSA-3px3-54cx-rmw9

Agent brief

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# Patch Next advisory brief: CVE-2026-83609

Advisory: xmldom: Creation-time XML Name/QName validation is bypassable via an embedded line terminator, allowing injection on the default serialization path
IDs: CVE-2026-83609, GHSA-3px3-54cx-rmw9
Record: https://patchnext.com/advisories/cve-2026-83609 (revision 4, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @xmldom/xmldom 0.9.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @xmldom/xmldom: affected >= 0.9.0, <= 0.9.11; fixed in 0.9.12

## Suggested inspection (read-only)
- `npm ls @xmldom/xmldom --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 @xmldom/xmldom.
- 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-3px3-54cx-rmw9 (GitHub-reviewed advisory GHSA-3px3-54cx-rmw9 lists affected ranges: npm @xmldom/xmldom >=0.9.0 <=0.9.11)
- Verified: https://osv.dev/vulnerability/GHSA-3px3-54cx-rmw9 (OSV record GHSA-3px3-54cx-rmw9 lists affected ranges: npm @xmldom/xmldom >=0.9.0 <0.9.12 (fixed))

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