Mercury: Stored / DOM Cross-Site Scripting (XSS): mr.Markdown renders untrusted content as raw, unsanitized HTML

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-111059: 0.28% estimated exploitation activity in the next 30 days; percentile 20.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Mercury turns Jupyter notebooks into shared web apps/dashboards. The mr.Markdown widget converts its input to HTML with python-markdown and no sanitization step. MarkdownWidget is an ipywidgets.HTML widget, whose value is written to the page as raw HTML (via innerHTML) with no sanitization, so the result reaches the DOM verbatim. When an app passes untrusted data (database rows, user submissions, uploaded file contents, or an external/LLM API response) to mr.Markdown, HTML/JS in that data executes in the browser of whoever views the app — a data-driven stored/DOM-based XSS. This is a library-provided rendering sink that fails to neutralize output; it is triggered by ordinary, reasonable application code, not by an author mistake. Root cause mercury/md.py — MarkdownWidget.tohtml() (verified at v3.2.6, lines ~57–65): Two neutralization failures compound: 1. Markdown → HTML is unsanitized. python-markdown passes raw HTML through by default: <img src=x onerror=…, <svg onload=…,…

Published by the source

19 Oct 2026, 17:01 UTC

Last modified by the source

19 Oct 2026, 17:15 UTC

Source last checked

26 Oct 2026, 13:55 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-2658-85cv-9wwq

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-2658-85cv-9wwq

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-2658-85cv-9wwq

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# Patch Next advisory brief: CVE-2026-111059

Advisory: Mercury: Stored / DOM Cross-Site Scripting (XSS): mr.Markdown renders untrusted content as raw, unsanitized HTML
IDs: CVE-2026-111059, GHSA-2658-85cv-9wwq
Record: https://patchnext.com/advisories/cve-2026-111059 (revision 3, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mercury 3.2.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mercury: affected >= 3.0.0, < 3.2.11; fixed in 3.2.11

## Suggested inspection (read-only)
- `python -m pip show mercury`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mercury.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2658-85cv-9wwq (GitHub-reviewed advisory GHSA-2658-85cv-9wwq lists affected ranges: PyPI mercury >=3.0.0 <3.2.11)
- Verified: https://osv.dev/vulnerability/GHSA-2658-85cv-9wwq (OSV record GHSA-2658-85cv-9wwq lists affected ranges: PyPI mercury >=3.0.0 <3.2.11 (fixed))

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