Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-07-06T21:00:38 showdown: Showdown: Cross-site scripting via unescaped metadata title allows arbitrary code execution 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N CWE-79

showdown contains a cross-site scripting vulnerability in metadata title handling that allows attackers to inject arbitrary HTML and JavaScript. When completeHTMLDocument option is enabled, unescaped less-than and greater-than characters in markdown frontmatter metadata are inserted directly into HTML title tags, enabling attackers to break out of the title context and execute malicious scripts in the rendered page.

A flaw was found in showdown. This cross-site scripting (XSS) vulnerability occurs in the metadata title handling when the `completeHTMLDocument` option is enabled. An attacker can exploit this by injecting unescaped less-than and greater-than characters into markdown frontmatter metadata. This allows the attacker to break out of the HTML title context and execute arbitrary HTML and JavaScript, potentially leading to information disclosure or arbitrary code execution in the user's browser.

Red Hat rates this flaw as Moderate. Exploitation requires two non-default showdown options enabled simultaneously: metadata and completeHTMLDocument, both of which default to false. Red Hat products that ship showdown do not enable completeHTMLDocument in their default configurations, which reduces the likelihood of exploitation. Do not enable showdown's completeHTMLDocument option when processing untrusted markdown input. If the option is required, sanitize metadata values before passing them to the converter. Cryostat 4 Fix deferred cryostat-openshift-console-plugin-npm Cryostat 4 Fix deferred showdown Multicluster Engine for Kubernetes Under investigation multicluster-engine/console-mce-rhel9 Node HealthCheck Operator Fix deferred workload-availability/node-healthcheck-must-gather-rhel9 Node HealthCheck Operator Fix deferred workload-availability/node-healthcheck-operator-bundle Node HealthCheck Operator Fix deferred workload-availability/node-healthcheck-rhel9-operator Red Hat 3scale API Management Platform 2 Fix deferred 3scale-amp21/system Red Hat 3scale API Management Platform 2 Fix deferred 3scale-amp22/system Red Hat 3scale API Management Platform 2 Fix deferred 3scale-amp2/system-rhel7 Red Hat 3scale API Management Platform 2 Fix deferred 3scale-amp2/system-rhel8 Red Hat 3scale API Management Platform 2 Fix deferred 3scale-amp2/system-rhel9 Red Hat Advanced Cluster Management for Kubernetes 2 Under investigation rhacm2/console-rhel9 Red Hat Ansible Automation Platform 2 Under investigation automation-eda-controller Red Hat Ansible Automation Platform 2 Under investigation automation-gateway Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-dashboard-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mlflow-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-automl-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-autorag-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-eval-hub-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-gen-ai-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-maas-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-mlflow-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-mod-arch-model-registry-rhel9 Red Hat OpenShift Container Platform 4 Fix deferred openshift4/ose-console Red Hat OpenShift Container Platform 4 Fix deferred openshift4/ose-console-rhel9 Red Hat OpenShift Container Platform 4 Fix deferred openshift4/ose-monitoring-plugin-rhel8 Red Hat OpenShift Virtualization 4 Fix deferred container-native-virtualization/kubevirt-console-plugin Red Hat OpenShift Virtualization 4 Fix deferred container-native-virtualization/kubevirt-console-plugin-rhel9 Red Hat Quay 3 Fix deferred quay/quay-rhel8 Red Hat Quay 3 Fix deferred quay/quay-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-59711 https://nvd.nist.gov/vuln/detail/CVE-2026-59711 https://github.com/showdownjs/showdown https://github.com/showdownjs/showdown/issues/1047 https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument