Vulnerability · Published Jul 6, 2026 · Assigned by VulnCheck

CVE-2026-59710showdown - Stored XSS via Unescaped Table Header ID Attribute Injection

Medium 6.1

In plain English

A medium-severity cross-site scripting in showdown from showdown. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities).

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.3%top 72.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

showdown contains a stored cross-site scripting vulnerability in the parseHeaders function of src/subParsers/makehtml/tables.js that fails to properly escape table header ID attributes. Attackers can inject arbitrary HTML and script-executing SVG elements through double-quote characters in markdown table headers, achieving stored XSS when untrusted markdown is rendered with the default github flavor configuration.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	showdown	no fix listed	GHSA-22g5-r2x5-97cx

Affected products (as reported)

Vendor	Product	Versions
showdown	showdown	0 – through 2.1.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References

GitHub Issue issue-tracking
Product product
https://github.com/showdownjs/showdown/commit/e5cab1e9a5dcea2bb3cbf888863fa7e65ab37edf patch
https://www.vulncheck.com/advisories/showdown-stored-xss-via-unescaped-table-header-id-attribute-injection third-party-advisory