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

{
  "id": "3d1483f4d9390de76a292636b0b54a864862147a0bca0a416e74e644a5a31bab",
  "url": "https://osv.dev/vulnerability/GHSA-2658-85cv-9wwq",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mercury: Stored / DOM Cross-Site Scripting (XSS): mr.Markdown renders untrusted content as raw, unsanitized HTML",
    "summary": "## 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._to_html()` (verified at v3.2.6, lines ~57–65): ```python def _to_html(self, text: str) -> str: if md_lib is not None: body = md_lib.markdown(text) # python-markdown: passes raw HTML through else: body = f\"{escape(text)} \" # escape() is ONLY the md-lib-absent fallback return self._apply_inline_theme(body) # regex styling — adds style=, removes nothing ``` Two neutralization failures compound: 1. **Markdown → HTML is unsanitized.** `python-markdown` passes raw HTML through by default: ``, ``, and `javascript:` links survive verbatim. There is no `bleach`/`nh3` allowlist anywhere in the package. `_apply_inline_theme()` only injects inline `style=` attributes via regex;",
    "evidence": "osv:GHSA-2658-85cv-9wwq",
    "products": [
      {
        "name": {
          "value": "mercury",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "3.2.11",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "3.0.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.0.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.0.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.4",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.5",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.10",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.3",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.4",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.5",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.6",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.7",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.8",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.9",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-2658-85cv-9wwq",
      "aliases": [
        "CVE-2026-111059",
        "GHSA-2658-85cv-9wwq"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.0.0"
                },
                {
                  "fixed": "3.2.11"
                }
              ]
            }
          ],
          "package": {
            "name": "mercury",
            "purl": "pkg:pypi/mercury",
            "ecosystem": "PyPI"
          },
          "versions": [
            "3.0.0",
            "3.0.1",
            "3.0.2",
            "3.1.0",
            "3.1.1",
            "3.1.2",
            "3.1.4",
            "3.1.5",
            "3.2.0",
            "3.2.1",
            "3.2.10",
            "3.2.2",
            "3.2.3",
            "3.2.4",
            "3.2.5",
            "3.2.6",
            "3.2.7",
            "3.2.8",
            "3.2.9"
          ],
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-2658-85cv-9wwq/GHSA-2658-85cv-9wwq.json"
          }
        }
      ],
      "modified": "2026-10-19T17:15:04.101718667Z",
      "provider": "osv",
      "references": [
        "https://github.com/mljar/mercury/security/advisories/GHSA-2658-85cv-9wwq",
        "https://github.com/mljar/mercury/commit/c798a85924e6614c6fea7afe5a560e4554a1d09b",
        "https://github.com/mljar/mercury",
        "https://github.com/mljar/mercury/releases/tag/v3.2.11"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-116",
          "CWE-79"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-19T17:01:20Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-111059",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 375520,
  "published_at": "2026-10-19T17:01:20+00:00"
}