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MEDIUM severity

CVE-2018-5773 — markdown2

MEDIUMFix: trentm/python-markdown2#303

CVE-2018-5773 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in markdown2. A fix is available for markdown2 — see the affected versions and patch details below.

markdown2 is vulnerable to cross-site scripting

Also known asGHSA-p6h9-gw49-rqm4PYSEC-2018-13
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs56th percentile — riskier than 56% of all scored CVEsHighest risk
0.00%0.44%0.88%1.32%0.4%0.8%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2018-5773 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐍markdown2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

An issue was discovered in markdown2 (aka python-markdown2) through 2.3.5. The safe_mode feature, which is supposed to sanitize user input against XSS, is flawed and does not escape the input properly. With a crafted payload, XSS can be triggered, as demonstrated by omitting the final '>' character from an IMG tag.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPImarkdown2all versions2.3.6pip install --upgrade 'markdown2==2.3.6'

Affected Products

1 product · 1 configurations
Application
python-markdown2python-markdown2_project
≤ 2.3.5
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for markdown2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update markdown2 to 2.3.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-5773 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

An issue was discovered in markdown2 (aka python-markdown2) through 2.3.5. The safe_mode feature, which is supposed to sanitize user input against XSS, is flawed and does not escape the input properly. With a crafted payload, XSS can be triggered, as demonstrated by omitting the final '>' character from an IMG tag.
O3 Security · Impact-Aware SCA

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CVE-2018-5773: markdown2 XSS — Fixed in 2.3.6