CVE-2026-41674

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. In @xmldom/xmldom prior to versions 0.9.10 and 0.8.13 and xmldom version 0.6.0 and prior, the package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it. This issue has been patched in versions @xmldom/xmldom versions 0.9.10 and 0.8.13.

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. In @xmldom/xmldom prior to versions 0.9.10 and 0.8.13 and xmldom version 0.6.0 and prior, the package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it. This issue has been patched in versions @xmldom/xmldom versions 0.9.10 and 0.8.13.

Summary

The package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it.

Details

DOMImplementation.createDocumentType(qualifiedName, publicId, systemId, internalSubset) validates only qualifiedName against the XML QName production. The remaining three arguments are stored as-is with no validation.

The XMLSerializer emits DocumentType nodes as:

<!DOCTYPE name[ PUBLIC pubid][ SYSTEM sysid][ [internalSubset]]>

All fields are pushed into the output buffer verbatim — no escaping, no quoting added.

internalSubset injection: The serializer wraps internalSubset with [ and ]. A value containing ]> closes the internal subset and the DOCTYPE declaration at the injection point. Any content after ]> in internalSubset appears outside the DOCTYPE in the serialized output as raw XML markup. Reported by @TharVid (GHSA-f6ww-3ggp-fr8h). Affected: @xmldom/xmldom ≥ 0.9.0 via createDocumentType API; 0.8.x only via direct property write.

publicId injection: The serializer emits publicId verbatim after PUBLIC with no quoting added. A value containing an injected system identifier (e.g., "pubid" SYSTEM "evil") breaks the intended quoting context, injecting a fake SYSTEM entry into the serialized DOCTYPE declaration. Identified during internal security research. Affected: both branches, all versions back to 0.1.0.

systemId injection: The serializer emits systemId verbatim. A value containing > terminates the DOCTYPE declaration early; content after > appears as raw XML markup outside the DOCTYPE context. Identified during internal security research. Affected: both branches, all versions back to 0.1.0.

The parse path is safe: the SAX parser enforces the PubidLiteral and SystemLiteral grammar productions, which exclude the relevant characters, and the internal subset parser only accepts a subset it can structurally validate. The vulnerability is reachable only through programmatic createDocumentType calls with attacker-controlled arguments.

Affected code

lib/dom.js — createDocumentType (lines 898–910):

createDocumentType: function (qualifiedName, publicId, systemId, internalSubset) {
    validateQualifiedName(qualifiedName);          // only qualifiedName is validated
    var node = new DocumentType(PDC);
    node.name = qualifiedName;
    node.nodeName = qualifiedName;
    node.publicId = publicId || '';               // stored verbatim
    node.systemId = systemId || '';               // stored verbatim
    node.internalSubset = internalSubset || '';   // stored verbatim
    node.childNodes = new NodeList();
    return node;
},

lib/dom.js — serializer DOCTYPE case (lines 2948–2964):

case DOCUMENT_TYPE_NODE:
    var pubid = node.publicId;
    var sysid = node.systemId;
    buf.push(g.DOCTYPE_DECL_START, ' ', node.name);
    if (pubid) {
        buf.push(' ', g.PUBLIC, ' ', pubid);
        if (sysid && sysid !== '.') {
            buf.push(' ', sysid);
        }
    } else if (sysid && sysid !== '.') {
        buf.push(' ', g.SYSTEM, ' ', sysid);
    }
    if (node.internalSubset) {
        buf.push(' [', node.internalSubset, ']');  // internalSubset emitted verbatim
    }
    buf.push('>');
    return;

PoC

internalSubset injection

const { DOMImplementation, XMLSerializer } = require('@xmldom/xmldom');

const impl = new DOMImplementation();
const doctype = impl.createDocumentType(
    'root',
    '',
    '',
    ']><injected/><![CDATA['
);
const doc = impl.createDocument(null, 'root', doctype);
const xml = new XMLSerializer().serializeToString(doc);
console.log(xml);
// <!DOCTYPE root…

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. In @xmldom/xmldom prior to versions 0.9.10 and 0.8.13 and xmldom version 0.6.0 and prior, the package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it. This issue has been patched in versions @xmldom/xmldom versions 0.9.10 and 0.8.13.

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. In @xmldom/xmldom prior to versions 0.9.10 and 0.8.13 and xmldom version 0.6.0 and prior, the package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it. This issue has been patched in versions @xmldom/xmldom versions 0.9.10 and 0.8.13.

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. In @xmldom/xmldom prior to versions 0.9.10 and 0.8.13 and xmldom version 0.6.0 and prior, the package serializes DocumentType node fields (internalSubset, publicId, systemId) verbatim without any escaping or validation. When these fields are set programmatically to attacker-controlled strings, XMLSerializer.serializeToString can produce output where the DOCTYPE declaration is terminated early and arbitrary markup appears outside it. This issue has been patched in versions @xmldom/xmldom versions 0.9.10 and 0.8.13.