CVE-2026-83609: xmldom XML name validation bypass via line terminator

CVE-2026-83609 · Severity: high · CVSS 4 · Published 2026-09-01

xmldom is a JavaScript library that parses and serializes XML documents. A validation bypass allows attackers to inject malicious XML markup (such as script tags) by embedding hidden line terminator characters in element and attribute names. When the document is serialized for output, the injected markup is emitted as part of the XML, potentially leading to cross-site scripting (XSS) attacks if the output is processed as HTML.

Technologies: @xmldom/xmldom (npm). Vendors: npm.

Quick answers

Is CVE-2026-83609 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-83609 being exploited in the wild.
How severe is CVE-2026-83609?
High severity, with a CVSS score of 4, published 1 September 2026.
Which products and versions are affected?
@xmldom/xmldom (npm) >= 0.9.0, <= 0.9.11, SEMVER:introduced=0.9.0,fixed=0.9.12.
Is there a fix for CVE-2026-83609?
Yes. @xmldom/xmldom (npm): upgrade to 0.9.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-83609 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-83609?
Check whether you run @xmldom/xmldom (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @xmldom/xmldom (npm): upgrade to 0.9.12 or later
    npm install @xmldom/xmldom@0.9.12

Technical details

The vulnerability is a regex anchor bypass (CWE-625). The library uses a shared regexp builder that compiles name-validation patterns with the `m` (multiline) flag, causing `^…$` anchors to match line boundaries rather than string boundaries. The validateQualifiedName and createAttribute methods test names against QName_exact using `.test()`, which accepts any name whose first line is valid and leaves subsequent lines unconstrained. An attacker can inject a line terminator (U+000A, U+000D, U+2028, or U+2029) followed by XML breakout markup (e.g., `a\n><script>x</script`) that passes validation but is emitted verbatim during serialization. The fix enforces whole-string validation by rejecting names containing any line terminator, preventing the malformed name from entering the DOM in the first place.

Affected products

  • xmldom @xmldom/xmldom 0.9.0 through 0.9.11

Identifiers

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

Timeline

  • 2026-08-21: disclosed: Initial publication of the security advisory
  • 2026-09-08: patched: Fix released in version 0.9.12

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.