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Fencer Vulns
medium 6.1

CVE-2026-59710 json

showdown - Stored XSS via Unescaped Table Header ID Attribute Injection

published 2026-07-06 4 mo ago modified 2026-09-10 1 mo ago also GHSA-22g5-r2x5-97cx , EUVD-2026-41954

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

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.

Patch / fix

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-59710 updated cvss 6.1

showdown: Showdown: Stored Cross-Site Scripting via unescaped table header ID attributes in markdown

  • Red Hat Cryostat 4 showdown 2.1.0, cryostat-openshift-console-plugin-npm Red Hat Multicluster Engine for Kubernetes multicluster-engine/console-mce-rhel9 Red Hat Node HealthCheck Operator workload-availability/node-healthcheck-rhel9-operator, workload-availability/node-healthcheck-operator-bundle, workload-availability/node-healthcheck-must-gather-rhel9 Red Hat 3scale API Management Platform 2 3scale-amp2/system-rhel7 Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/console-rhel9 Red Hat Ansible Automation Platform 2 automation-gateway 2.5.20260422-3.el9ap, automation-eda-controller 1.0.11-1.el9ap
    +4 more products
    Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-automl-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-mod-arch-mlflow-rhel9, +3 more Red Hat OpenShift Container Platform 4 openshift4/ose-console, openshift4/ose-console-rhel9, openshift4/ose-monitoring-plugin-rhel8 Red Hat OpenShift Virtualization 4 container-native-virtualization/kubevirt-console-plugin, container-native-virtualization/kubevirt-console-plugin-rhel9 Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/showdownjs/showdown/issues/1046 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 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
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CNA 4.0 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/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:X/V:X/RE:X/U:X
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm showdown
<=2.1.0
 no fix listed

Affected products

  • showdown showdown

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.