` context when the full document is rendered. This allows for arbitrary script execution in the context of the web application. The vulnerability is present in versions up to and including 2.1.0. ## Affected products - showdownjs showdown <= 2.1.0 ## Identifiers - CVE-2026-59711 - GHSA-cr32-g25g-vxjj ## Timeline - 2026-03-12: disclosed: Issue reported on GitHub repository - 2026-07-06: advisory: NVD and GitHub Advisory published ## References - [https://github.com/showdownjs/showdown/issues/1047](https://github.com/showdownjs/showdown/issues/1047) - [https://github.com/showdownjs/showdown](https://github.com/showdownjs/showdown) - [https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument](https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument) - [https://github.com/showdownjs/showdown/commit/184a3e4e97f90e075c4512f2c4c06dcf655e91b7](https://github.com/showdownjs/showdown/commit/184a3e4e97f90e075c4512f2c4c06dcf655e91b7) ## Related threats - [Showdown stored XSS in table header ID attributes](https://junglewise.ai/threats/cve-2026-59710-showdown-stored-xss-in-table-header-id-attributes) - [Showdown vulnerable to Regular Expression Denial of Service (ReDoS) in link/anchor parsing](https://junglewise.ai/threats/cve-2024-1899-showdown-vulnerable-to-regular-expression-denial-of-service-redos) - [showdown reverse tabnabbing in anchor tags](https://junglewise.ai/threats/showdown-reverse-tabnabbing-in-anchor-tags-ec12f775)

# CVE-2026-59711: showdownjs showdown XSS in metadata title handling Source: https://junglewise.ai/threats/cve-2026-59711-showdownjs-showdown-xss-in-metadata-title-handling Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats Published: 2026-07-06. Updated: 2026-08-07 License: CC BY 4.0 with a link back CVE-2026-59711 · Severity: medium · CVSS 6.1 · Published 2026-07-06 Showdown, a popular library used to convert Markdown text into HTML, contains a security flaw in how it handles document titles. If a website uses Showdown to generate full web pages from user-provided content, an attacker could provide a specially crafted title that injects malicious scripts into the page. This could allow the attacker to steal user session information, perform actions on behalf of users, or deface the website for anyone viewing the rendered content. Technologies: [showdown (npm)](https://junglewise.ai/threats/technologies/showdown). Vendors: [npm](https://junglewise.ai/threats/vendors/npm). ## Quick answers **Is CVE-2026-59711 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59711 being exploited in the wild. **How severe is CVE-2026-59711?** Medium severity, with a CVSS score of 6.1, published 6 July 2026. **Which products and versions are affected?** showdown (npm) <= 2.1.0, SEMVER:introduced=0,last_affected=2.1.0. **Is there a fix for CVE-2026-59711?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it. **How is CVE-2026-59711 attacked?** It is attacked over the network, in a software library. **Am I affected by CVE-2026-59711?** Check whether you run showdown (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. ## Technical details A cross-site scripting (XSS) vulnerability exists in Showdown's metadata parsing logic within `src/subParsers/makehtml/metadata.js` and `src/subParsers/makehtml/completeHTMLDocument.js`. When both the `metadata` and `completeHTMLDocument` options are enabled, the library fails to escape less-than (<) and greater-than (>) characters in the YAML frontmatter 'title' field. An attacker can provide markdown containing a title like ``, which breaks out of the HTML `` context when the full document is rendered. This allows for arbitrary script execution in the context of the web application. The vulnerability is present in versions up to and including 2.1.0. ## Affected products - showdownjs showdown <= 2.1.0 ## Identifiers - CVE-2026-59711 - GHSA-cr32-g25g-vxjj ## Timeline - 2026-03-12: disclosed: Issue reported on GitHub repository - 2026-07-06: advisory: NVD and GitHub Advisory published ## References - [https://github.com/showdownjs/showdown/issues/1047](https://github.com/showdownjs/showdown/issues/1047) - [https://github.com/showdownjs/showdown](https://github.com/showdownjs/showdown) - [https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument](https://www.vulncheck.com/advisories/showdown-cross-site-scripting-via-unescaped-metadata-title-in-completehtmldocument) - [https://github.com/showdownjs/showdown/commit/184a3e4e97f90e075c4512f2c4c06dcf655e91b7](https://github.com/showdownjs/showdown/commit/184a3e4e97f90e075c4512f2c4c06dcf655e91b7) ## Related threats - [Showdown stored XSS in table header ID attributes](https://junglewise.ai/threats/cve-2026-59710-showdown-stored-xss-in-table-header-id-attributes) - [Showdown vulnerable to Regular Expression Denial of Service (ReDoS) in link/anchor parsing](https://junglewise.ai/threats/cve-2024-1899-showdown-vulnerable-to-regular-expression-denial-of-service-redos) - [showdown reverse tabnabbing in anchor tags](https://junglewise.ai/threats/showdown-reverse-tabnabbing-in-anchor-tags-ec12f775)