# 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.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **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:** Yes
- **Published:** 6 Jul 2026
- **Updated:** 7 Jul 2026
- **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, MINI-wpvr-vmp4-hc9v

## 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 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-59711?

2 open source packages ship an affected version, including showdown.


| Package | Ecosystem | 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.

## Is CVE-2026-59711 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59711 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-59711 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59711 exists.

Affected packages and fixed versions:
- showdown (npm): affected all versions up to 2.1.0; no fix listed
- showdown (npm): affected all versions up to 2.1.0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-59711/ (Markdown: https://insights.sbomify.com/CVE-2026-59711/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59711
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59711
- OSV: https://osv.dev/vulnerability/CVE-2026-59711

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59711/
Summaries are generated and may contain mistakes; the official description above is the record.