What is CVE-2026-104477?

CVE-2026-104477 is a medium-severity vulnerability in Showdownjs Showdown, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-10-03.

How severe is CVE-2026-104477?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Showdownjs Showdown

CVE-2026-104477

Showdown through 2.1.0 contains a cross-site scripting vulnerability in the makehtml link and image subparsers, which fail to escape double quotes in destination URLs placed into href and src attributes. Attackers can craft markdown links or images containing a double quote followed by onerror or onmouseover handlers to execute script when victims view rendered HTML.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-10-03.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Showdownjs Showdown

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/showdownjs/showdown/commit/4fb992cd26631c108ec0410342630c80207ec7c6 (patch)
github.com/showdownjs/showdown (product)
www.vulncheck.com/advisories/showdown-through-2.1.0-xss-via-unescaped-quote-in-… (third-party-advisory)

Frequently asked questions

What is CVE-2026-104477?: CVE-2026-104477 is a medium-severity vulnerability in Showdownjs Showdown, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-10-03.
How severe is CVE-2026-104477?: Medium severity. CVSS v3 base score is 6.1 out of 10.