CVE-2026-83612: xmldom HTML Raw-text Closing-tag Case Mismatch Vulnerability

Q: What is CVE-2026-83612?

CVE-2026-83612 is a security vulnerability in xmldom involving HTML raw-text closing-tag case mismatch causes output amplification under CWE-400: Uncontrolled Resource Consumption.

Q: Which xmldom versions are affected?

Affected versions include releases prior to 0.9.12 across affected packages: @xmldom/xmldom.

Q: What version fixes CVE-2026-83612?

Upgrading to 0.9.12 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is @xmldom/xmldom affected?

Yes, @xmldom/xmldom is affected in releases prior to 0.9.12. Upgrade your dependency to 0.9.12 or later.

Q: What CWE is associated with CVE-2026-83612?

CVE-2026-83612 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).

Q: How can I check npm dependencies for CVE-2026-83612?

Run the dependency tree command: 'npm ls @xmldom/xmldom'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

HIGH

Advisory Identifier: GHSA-6mj3-qw4j-hgrw

CWE-400 CWE-178

Published 2026-09-08

Advisory Summary

CVE-2026-83612 is a HIGH html raw-text closing-tag case mismatch vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting xmldom libraries in the npm ecosystem. The issue involves html raw-text closing-tag case mismatch causes output amplification. Remediation is available by upgrading affected packages to version 0.9.12.

CVE-2026-83612 at a Glance

CVE Identifier CVE-2026-83612

GHSA Identifier GHSA-6mj3-qw4j-hgrw

Severity HIGH

CVSS v3.1 Base Score N/A

CWE Classification CWE-400: Uncontrolled Resource Consumption

Affected Product xmldom

Package Ecosystem npm

Published Date 2026-09-08

Last Updated 2026-09-08

How to Fix CVE-2026-83612

To remediate this vulnerability, upgrade all affected xmldom dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@xmldom/xmldom fixed: 0.9.12

npm install @xmldom/xmldom@0.9.12

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

npm ls @xmldom/xmldom

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-83612, inspect your project dependencies using npm:

npm ls @xmldom/xmldom

Analyze the terminal output to locate any version of xmldom in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.9.12), your application is affected.

Note: The npm ls @xmldom/xmldom command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In xmldom, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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 text backwards from the start of the document instead of the element's content. The function then returns `-1` to the parse loop, which cannot advance normally and falls back to character-by-character reprocessing. Every raw-text element re-captures all source text preceding it, so output grows as O(n²) in the number of such elements. ### Root Cause 1. **Case-sensitive close-tag search** (`lib/sax.js:549`): `source.indexOf('</' + tagName + '>', elStartEnd)` does not fold case, contrary to the WHATWG HTML RAWTEXT end-tag-name rule. 2. **Unguarded `-1`** (`lib/sax.js:550`): `source.substring(elStartEnd + 1, elEndStart)` runs even when `elEndStart === -1`, extracting text backwards from position 0. 3. **Unstable progression** (`lib/sax.js:556`): the function returns `elEndStart` (`-1`), driving repeated character-by-character fallback in the parse loop. ## Affected Versions Only the `0.9.x` line is affected — the amplification was introduced in `0.9.0-beta.1` when `parseHtmlSpecialContent` was refactored, and remains through `0.9.11`. The `0.8.x` line is **not** affected: its older `parseHtmlSpecialContent` does not amplify, despite sharing the same case-sensitive `indexOf`. ## Proof of Concept ```js const { DOMParser, XMLSerializer } = require('@xmldom/xmldom'); const n = 1000; const payload = '<html><body>' + '<script>x</ScRiPt>'.repeat(n) + '</body></html>'; const doc = new DOMParser().parseFromString(payload, 'text/html'); const out = new XMLSerializer().serializeToString(doc); console.log(payload.length, out.length, (out.length / payload.length).toFixed(1) + 'x'); // 18026 9037063 501.3x — an 18 KB input yields ~9 MB of output ``` Output size grows quadratically with the number of case-mismatched raw-text elements: ``` Repeats | Input len | Output len | Ratio 1 | 44 | 109 | 2.5x 100 | 1826 | 93763 | 51.3x 500 | 9026 | 2268563 | 251.3x 1000 | 18026 | 9037063 | 501.3x 2000 | 36026 | 36074063 | 1001.3x ``` Proof of Concept from @KarimTantawey (tested with `script`); the same amplification occurs for `style`, `textarea`, and `title`. ## Impact Small attacker payloads can force disproportionate CPU and memory usage in services that parse and serialize untrusted HTML via xmldom. The quadratic growth means a modest-sized input (tens of kilobytes) can produce output in the tens or hundreds of megabytes, potentially exhausting memory or causing timeouts. The attack only requires HTML mode (`text/html` MIME type) and mixed-case closing tags for any of the four raw-text element types. No special configuration or error handler setup is needed. ## Severity note The CVSS 4.0 vector scores availability only (`VA:H`, with `VC:N/VI:N`): the flaw neither discloses nor corrupts data, but a small untrusted HTML input (tens of KB) can force output and memory in the tens to hundreds of MB, enough to exhaust a service's heap or stall its event loop. It is reachable with no authentication, configuration, or error-handler setup — only that the application parses untrusted `text/html` and serializes the result. ## Fix Applied The raw-text closing tag is now matched case-insensitively in HTML raw-text mode (per the WHATWG HTML [RAWTEXT end-tag rule](https://html.spec.whatwg.org/multipage/parsing.html#rawtext-end-tag-name-state)), and a missing closing tag is handled explicitly, removing the quadratic output amplification. Output for well-formed input is unchanged. Non-breaking; 0.9.x-only.

CVE-2026-83612 Affected xmldom Versions

1 component(s)

Fixed Versions:

0.9.12

Product / Package	Ecosystem	Affected Versions	Fixed Version
@xmldom/xmldom npm/@xmldom/xmldom	npm	≥ 0.9.0-beta.1 < 0.9.12	0.9.12

References

GitHub Advisory / Wiki ADVISORY

https://github.com/xmldom/xmldom/security/advisories/GHSA-6mj3-qw4j-hgrw

NVD — CVE-2026-83612 NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-83612

xmldom Source Repository REPOSITORY

https://github.com/xmldom/xmldom/pull/1071

Security Fix Commit FIX COMMIT

https://github.com/xmldom/xmldom/commit/7ced40c06c28d151e996a97045018c3559ae4707

xmldom Source Repository REPOSITORY

https://github.com/xmldom/xmldom

xmldom Release RELEASE

https://github.com/xmldom/xmldom/releases/tag/0.9.12

Frequently Asked Questions

What is CVE-2026-83612?

CVE-2026-83612 is a security vulnerability in xmldom involving HTML raw-text closing-tag case mismatch causes output amplification under CWE-400: Uncontrolled Resource Consumption.

Which xmldom versions are affected?

Affected versions include releases prior to 0.9.12 across affected packages: @xmldom/xmldom.

What version fixes CVE-2026-83612?

Upgrading to 0.9.12 (or the latest patched release for your respective branch) resolves the vulnerability.

Is @xmldom/xmldom affected?

Yes, @xmldom/xmldom is affected in releases prior to 0.9.12. Upgrade your dependency to 0.9.12 or later.

What CWE is associated with CVE-2026-83612?

CVE-2026-83612 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).

How can I check npm dependencies for CVE-2026-83612?

Run the dependency tree command: 'npm ls @xmldom/xmldom'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6mj3-qw4j-hgrw",
  "modified" : "2026-09-08T20:59:54Z",
  "published" : "2026-09-08T20:59:54Z",
  "aliases" : [ "CVE-2026-83612" ],
  "summary" : "xmldom: HTML raw-text closing-tag case mismatch causes output amplification",
  "details" : "## Summary\n\nIn HTML mode (`text/html`), a raw-text element (`script`, `style`, `textarea`, `title`) whose closing\ntag differs in case from its opening tag (e.g. `</ScRiPt>` for `<script>`) is mishandled by the\nparser, producing quadratic (O(n²)) output growth — a small crafted document parses and serializes\ninto output orders of magnitude larger, exhausting CPU and memory. A modest input of tens of KB can\ntherefore cause a denial of service in any service that parses untrusted HTML with xmldom. Only HTML\nmode is affected.\n\n## Details\n\nThe parser calls `parseHtmlSpecialContent` for each raw-text element in HTML mode, matched via\n`isHTMLRawTextElement` / `isHTMLEscapableRawTextElement` (so all four types — `script`, `style`,\n`textarea`, `title` — are in scope). It searches for the element's closing tag with\n`source.indexOf('</' + tagName + '>', elStartEnd)`, a byte-for-byte case-sensitive match. A\nmixed-case closing tag never matches, so the search returns `-1`, and the following\n`source.substring(elStartEnd + 1, -1)` extracts text backwards from the start of the document\ninstead of the element's content. The function then returns `-1` to the parse loop, which cannot\nadvance normally and falls back to character-by-character reprocessing. Every raw-text element\nre-captures all source text preceding it, so output grows as O(n²) in the number of such elements.\n\n### Root Cause\n\n1. **Case-sensitive close-tag search** (`lib/sax.js:549`): `source.indexOf('</' + tagName + '>',\n   elStartEnd)` does not fold case, contrary to the WHATWG HTML RAWTEXT end-tag-name rule.\n2. **Unguarded `-1`** (`lib/sax.js:550`): `source.substring(elStartEnd + 1, elEndStart)` runs even\n   when `elEndStart === -1`, extracting text backwards from position 0.\n3. **Unstable progression** (`lib/sax.js:556`): the function returns `elEndStart` (`-1`), driving\n   repeated character-by-character fallback in the parse loop.\n\n## Affected Versions\n\nOnly the `0.9.x` line is affected — the amplification was introduced in `0.9.0-beta.1` when\n`parseHtmlSpecialContent` was refactored, and remains through `0.9.11`. The `0.8.x` line is **not**\naffected: its older `parseHtmlSpecialContent` does not amplify, despite sharing the same\ncase-sensitive `indexOf`.\n\n## Proof of Concept\n\n```js\nconst { DOMParser, XMLSerializer } = require('@xmldom/xmldom');\n\nconst n = 1000;\nconst payload = '<html><body>' + '<script>x</ScRiPt>'.repeat(n) + '</body></html>';\nconst doc = new DOMParser().parseFromString(payload, 'text/html');\nconst out = new XMLSerializer().serializeToString(doc);\nconsole.log(payload.length, out.length, (out.length / payload.length).toFixed(1) + 'x');\n// 18026 9037063 501.3x  — an 18 KB input yields ~9 MB of output\n```\n\nOutput size grows quadratically with the number of case-mismatched raw-text elements:\n\n```\nRepeats | Input len | Output len | Ratio\n1       | 44        | 109        | 2.5x\n100     | 1826      | 93763      | 51.3x\n500     | 9026      | 2268563    | 251.3x\n1000    | 18026     | 9037063    | 501.3x\n2000    | 36026     | 36074063   | 1001.3x\n```\n\nProof of Concept from @KarimTantawey (tested with `script`); the same amplification occurs for `style`,\n`textarea`, and `title`.\n\n## Impact\n\nSmall attacker payloads can force disproportionate CPU and memory usage in services that\nparse and serialize untrusted HTML via xmldom. The quadratic growth means a modest-sized input\n(tens of kilobytes) can produce output in the tens or hundreds of megabytes, potentially\nexhausting memory or causing timeouts.\n\nThe attack only requires HTML mode (`text/html` MIME type) and mixed-case closing tags for\nany of the four raw-text element types. No special configuration or error handler setup is needed.\n\n## Severity note\n\nThe CVSS 4.0 vector scores availability only (`VA:H`, with `VC:N/VI:N`): the flaw neither discloses\nnor corrupts data, but a small untrusted HTML input (tens of KB) can force output and memory in the\ntens to hundreds of MB, enough to exhaust a service's heap or stall its event loop. It is reachable\nwith no authentication, configuration, or error-handler setup — only that the application parses\nuntrusted `text/html` and serializes the result.\n\n## Fix Applied\n\nThe raw-text closing tag is now matched case-insensitively in HTML raw-text mode (per the WHATWG HTML\n[RAWTEXT end-tag rule](https://html.spec.whatwg.org/multipage/parsing.html#rawtext-end-tag-name-state)),\nand a missing closing tag is handled explicitly, removing the quadratic output amplification. Output\nfor well-formed input is unchanged. Non-breaking; 0.9.x-only.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@xmldom/xmldom"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.9.0-beta.1"
      }, {
        "fixed" : "0.9.12"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.11"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/xmldom/xmldom/security/advisories/GHSA-6mj3-qw4j-hgrw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-83612"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/xmldom/xmldom/pull/1071"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/xmldom/xmldom/commit/7ced40c06c28d151e996a97045018c3559ae4707"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/xmldom/xmldom"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/xmldom/xmldom/releases/tag/0.9.12"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-178", "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T20:59:54Z",
    "nvd_published_at" : "2026-09-01T15:17:39Z"
  }
}

CVSS V4

N/A HIGH

Attack Vector N/A

Attack Complexity N/A

Privileges Required N/A

User Interaction N/A

Scope N/A

Confidentiality N/A

Integrity N/A

Availability N/A

Vector String

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

Advisory Metadata

Source ID: GHSA-6mj3-qw4j-hgrw
Schema Version: 1.4.0
Published: 2026-09-08 20:59
Last Modified: 2026-09-08 20:59
Database Record File: advisories/github-reviewed/2026/09/GHSA-6mj3-qw4j-hgrw/GHSA-6mj3-qw4j-hgrw.json