CVE-2026-59711 showdown - Cross-Site Scripting via Unescaped Metadata Title in completeHTMLDocument
Attackers can inject malicious scripts via unescaped metadata titles in showdown when the completeHTMLDocument option is enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-59711?
CVE-2026-59711 is a medium-severity cross-site scripting vulnerability in showdown, published on 6 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-59711?
2 open source packages ship an affected version, including showdown.
| Package | Affected | Fixed in |
|---|---|---|
showdown npm | All versions to 2.1.0 | None |
showdown npm | All versions to 2.1.0 | None |
How do I fix CVE-2026-59711?
Apply the vendor's patch.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-59711 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59711 exists.
Sources
Also known as GHSA-cr32-g25g-vxjj, MINI-369g-jcwf-xgr8, MINI-gph8-27j8-xmfh, MINI-qx3p-mm3v-8h96, MINI-r2mv-3q82-rr4h, MINI-vqrq-5w35-mfh5 and 1 more.