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Advisory severityMedium6.1Red Hat Linux

Medium [CVE-2026-59711] Cross-site scripting via unescaped metadata title allows arbitrary code execution

This medium-severity Red Hat Linux advisory covers CVE-2026-59711 affecting Multicluster Engine for Kubernetes, Node HealthCheck Operator, Red Hat 3scale API Management Platform 2.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-59711 Source published Source updated

VulniPulse record published Record updated

CVE-2026-59711
Affected products & platforms
Red Hat LinuxUnclassified
Open source advisory

Summary

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. 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. Red Hat severity: Moderate — CVSS 6.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).

Weakness: CWE-79.

Is CVE-2026-59711 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-59711 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-59711?

The advisory VulniPulse tracks names no fixed release. Follow Red Hat's guidance for workarounds and updates.

Confirm against the vendor advisory before you patch.

Affected versions

No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.

Official advisory · high-confidence parse· fetched 13 days ago·verify at source

Fixed versions

No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.

Official advisory · high-confidence parse· fetched 13 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • 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.

Official advisory · high-confidence parse· fetched 13 days ago·verify at source

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