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Vulnerability record · CVE-2026-104477 · published 3 October 2026

CVE-2026-104477: Cross-site scripting vulnerability

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.

5.3 CVSS 4.0 Medium CWE-79 · Cross-site scripting Received
5.3CVSS 4.0 base score
-EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
3 Oct 2026Last modified by NVD

Description

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/showdownjs/showdown
https://github.com/showdownjs/showdown/commit/4fb992cd26631c108ec0410342630c80207ec7c6
https://www.vulncheck.com/advisories/showdown-through-2.1.0-xss-via-unescaped-quote-in-href-and-src-attributes

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Source: NIST National Vulnerability Database (record CVE-2026-104477), CISA KEV, FIRST EPSS. This page is refreshed as NVD updates the record.