CVE-2026-59710

showdown - Stored XSS via Unescaped Table Header ID Attribute Injection

State: Published
Severity: 5.3 Medium
Published: Jul 6, 2026
Updated: Jul 7, 2026
Reserved: Jul 6, 2026

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.

Scores

CVSS	Score	Vector	Source
4.0	5.3 Medium	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	VulnCheck
3.1	6.1 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N	VulnCheck

Weaknesses

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected Products

Product	Versions
showdownshowdown	2.1.0 and earlierAffected

References

GitHub Issueissue-tracking
Productproduct
https://github.com/showdownjs/showdown/commit/e5cab1e9a5dcea2bb3cbf888863fa7e65ab37edfpatch
https://www.vulncheck.com/advisories/showdown-stored-xss-via-unescaped-table-header-id-attribute-injectionthird-party-advisory

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