xmldom: HTML raw-text closing-tag case mismatch causes output amplification

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:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-83612: 0.52% estimated exploitation activity in the next 30 days; percentile 44.47 (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 In HTML mode (text/html), a raw-text element (script, style, textarea, title) whose closing tag differs in case from its opening tag (e.g. </ScRiPt for <script) is mishandled by the parser, producing quadratic (O(n²)) output growth — a small crafted document parses and serializes into output orders of magnitude larger, exhausting CPU and memory. A modest input of tens of KB can therefore cause a denial of service in any service that parses untrusted HTML with xmldom. Only HTML mode is affected. Details The parser calls parseHtmlSpecialContent for each raw-text element in HTML mode, matched via isHTMLRawTextElement / isHTMLEscapableRawTextElement (so all four types — script, style, textarea, title — are in scope). It searches for the element's closing tag with source.indexOf('</' + tagName + '', elStartEnd), a byte-for-byte case-sensitive match. A mixed-case closing tag never matches, so the search returns -1, and the following source.substring(elStartEnd + 1, -1) extracts…

Published by the source

8 Sep 2026, 20:59 UTC

Last modified by the source

8 Sep 2026, 21:15 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6mj3-qw4j-hgrw

2. Revision 3 · amended · 24 Oct 2026

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

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6mj3-qw4j-hgrw

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6mj3-qw4j-hgrw

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# Patch Next advisory brief: CVE-2026-83612

Advisory: xmldom: HTML raw-text closing-tag case mismatch causes output amplification
IDs: CVE-2026-83612, GHSA-6mj3-qw4j-hgrw
Record: https://patchnext.com/advisories/cve-2026-83612 (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-beta.1, <= 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-6mj3-qw4j-hgrw (GitHub-reviewed advisory GHSA-6mj3-qw4j-hgrw lists affected ranges: npm @xmldom/xmldom >=0.9.0-beta.1 <=0.9.11)
- Verified: https://osv.dev/vulnerability/GHSA-6mj3-qw4j-hgrw (OSV record GHSA-6mj3-qw4j-hgrw lists affected ranges: npm @xmldom/xmldom >=0.9.0-beta.1 <0.9.12 (fixed))

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