CVE-2026-55073

Summary

url_fetcher is WeasyPrint's documented mechanism for restricting resource loading - applications use it to block file://, internal hosts, etc. when rendering untrusted input.

Two write_pdf() channels ignore the document's url_fetcher and build a fresh default URLFetcher() instead. A restrictive fetcher set on HTML() is silently bypassed for:

• xmp_metadata=[url] - the URL is fetched and the bytes are embedded verbatim in the output PDF. This is an arbitrary local file read when the path is attacker-influenced.
• stylesheets=[url_or_path] - the sheet is fetched and applied. This is SSRF / arbitrary local-or-internal resource loading, and it is transitive: the permissive fetcher propagates through the whole @import / url() graph.

Applications affected are those that (1) run WeasyPrint server-side, (2) set a restrictive url_fetcher to block file:// or internal hosts, and (3) forward an attacker-influenced URL/path into either parameter - e.g. PDF rendering APIs, invoice/report generators, document SaaS.

Affected versions

All versions through current main - v69.0, commit 2945986160dedd97a7547be03805b667964e422a.

Root cause

select_source() defaults to a fresh fetcher when none is passed (weasyprint/urls.py):

def select_source(guess=None, filename=None, url=None, ..., url_fetcher=None, ...):
    ...
    if url_fetcher is None:
        url_fetcher = URLFetcher()

Five of the seven resource-loading sites thread the document's fetcher correctly:

• <link rel=stylesheet> in weasyprint/css/__init__.py
• <style> in weasyprint/css/__init__.py
• @import in weasyprint/css/__init__.py
• @font-face / local() in weasyprint/text/fonts.py
• @color-profile src in weasyprint/css/__init__.py
• images (<img>, CSS url(), SVG) in weasyprint/images.py

Two do not — they build a fresh default fetcher instead:

• write_pdf(xmp_metadata=[...]) in weasyprint/pdf/__init__.py
• write_pdf(stylesheets=[str]) in weasyprint/document.py

xmp_metadata - pdf/__init__.py calls select_source(url) with no url_fetcher, so the default fetcher runs regardless of what the caller configured:

if options['xmp_metadata']:
    for url in options['xmp_metadata']:
        result = select_source(url)          # no url_fetcher

stylesheets - document.py builds each sheet without passing url_fetcher, and CSS.__init__ then defaults to a fresh URLFetcher():

for css in options['stylesheets'] or []:
    if not hasattr(css, 'matcher'):
        css = CSS(                            # no url_fetcher=html.url_fetcher
            guess=css, media_type=html.media_type,
            font_config=font_config, counter_style=counter_style,
            color_profiles=color_profiles)

Because @import / url() inherit a CSS object's fetcher, the permissive fetcher propagates to the entire import graph - so the bypass is transitive.

Reproduction

Each script defines a Block fetcher that refuses every file://, writes its own fixture to a temp dir, and prints a boolean. True means the restrictive fetcher was bypassed. No external files or network needed.

1 - xmp_metadata= reads a file:// the fetcher blocks

import os, tempfile
from weasyprint import HTML
from weasyprint.urls import URLFetcher

class Block(URLFetcher):
    def fetch(self, url, headers=None):
        if url.lower().startswith('file:'):
            raise ValueError('blocked ' + url)
        return super().fetch(url, headers)

d = tempfile.mkdtemp()
path = os.path.join(d, 'secret.xmp')
open(path, 'wb').write(b'CANARY_XMP_LEAK_7f3a9c')
pdf = HTML(string='<p>hi</p>', url_fetcher=Block()).write_pdf(
    xmp_metadata=['file://' + path], pdf_variant='pdf/a-3b', uncompressed_pdf=True)
print('secret file leaked into PDF:', b'CANARY_XMP_LEAK_7f3a9c' in pdf)
# -> True

(pdf_variant='pdf/a-3b' makes the embedded bytes…

Summary

url_fetcher is WeasyPrint's documented mechanism for restricting resource loading - applications use it to block file://, internal hosts, etc. when rendering untrusted input.

Two write_pdf() channels ignore the document's url_fetcher and build a fresh default URLFetcher() instead. A restrictive fetcher set on HTML() is silently bypassed for:

• xmp_metadata=[url] - the URL is fetched and the bytes are embedded verbatim in the output PDF. This is an arbitrary local file read when the path is attacker-influenced.
• stylesheets=[url_or_path] - the sheet is fetched and applied. This is SSRF / arbitrary local-or-internal resource loading, and it is transitive: the permissive fetcher propagates through the whole @import / url() graph.

Applications affected are those that (1) run WeasyPrint server-side, (2) set a restrictive url_fetcher to block file:// or internal hosts, and (3) forward an attacker-influenced URL/path into either parameter - e.g. PDF rendering APIs, invoice/report generators, document SaaS.

Affected versions

All versions through current main - v69.0, commit 2945986160dedd97a7547be03805b667964e422a.

Root cause

select_source() defaults to a fresh fetcher when none is passed (weasyprint/urls.py):

def select_source(guess=None, filename=None, url=None, ..., url_fetcher=None, ...):
    ...
    if url_fetcher is None:
        url_fetcher = URLFetcher()

Five of the seven resource-loading sites thread the document's fetcher correctly:

• <link rel=stylesheet> in weasyprint/css/__init__.py
• <style> in weasyprint/css/__init__.py
• @import in weasyprint/css/__init__.py
• @font-face / local() in weasyprint/text/fonts.py
• @color-profile src in weasyprint/css/__init__.py
• images (<img>, CSS url(), SVG) in weasyprint/images.py

Two do not — they build a fresh default fetcher instead:

• write_pdf(xmp_metadata=[...]) in weasyprint/pdf/__init__.py
• write_pdf(stylesheets=[str]) in weasyprint/document.py

xmp_metadata - pdf/__init__.py calls select_source(url) with no url_fetcher, so the default fetcher runs regardless of what the caller configured:

if options['xmp_metadata']:
    for url in options['xmp_metadata']:
        result = select_source(url)          # no url_fetcher

stylesheets - document.py builds each sheet without passing url_fetcher, and CSS.__init__ then defaults to a fresh URLFetcher():

for css in options['stylesheets'] or []:
    if not hasattr(css, 'matcher'):
        css = CSS(                            # no url_fetcher=html.url_fetcher
            guess=css, media_type=html.media_type,
            font_config=font_config, counter_style=counter_style,
            color_profiles=color_profiles)

Because @import / url() inherit a CSS object's fetcher, the permissive fetcher propagates to the entire import graph - so the bypass is transitive.

Reproduction

Each script defines a Block fetcher that refuses every file://, writes its own fixture to a temp dir, and prints a boolean. True means the restrictive fetcher was bypassed. No external files or network needed.

1 - xmp_metadata= reads a file:// the fetcher blocks

import os, tempfile
from weasyprint import HTML
from weasyprint.urls import URLFetcher

class Block(URLFetcher):
    def fetch(self, url, headers=None):
        if url.lower().startswith('file:'):
            raise ValueError('blocked ' + url)
        return super().fetch(url, headers)

d = tempfile.mkdtemp()
path = os.path.join(d, 'secret.xmp')
open(path, 'wb').write(b'CANARY_XMP_LEAK_7f3a9c')
pdf = HTML(string='<p>hi</p>', url_fetcher=Block()).write_pdf(
    xmp_metadata=['file://' + path], pdf_variant='pdf/a-3b', uncompressed_pdf=True)
print('secret file leaked into PDF:', b'CANARY_XMP_LEAK_7f3a9c' in pdf)
# -> True

(pdf_variant='pdf/a-3b' makes the embedded bytes…

WeasyPrint helps web developers to create PDF documents. Prior to 70.0, server-side applications that configure a restrictive url_fetcher and pass attacker-influenced values to HTML.write_pdf() can have the restriction bypassed through the xmp_metadata or stylesheets options. In weasyprint/pdf/init.py, xmp_metadata calls select_source() without the document url_fetcher, allowing an accessible local file to be read and embedded verbatim in the output PDF. In weasyprint/document.py, stylesheets constructs CSS() without the document url_fetcher, allowing local or internal resource loading and propagating the permissive fetcher through nested CSS imports and url() references. The stylesheets channel applies fetched resources but does not by itself disclose stylesheet comments verbatim. This issue is fixed in version 70.0.

These are all security issues fixed in the python313-weasyprint-70.0-1.1 package on the GA media of openSUSE Tumbleweed.

This update for python-weasyprint fixes the following issues:

Changes in python-weasyprint:

• CVE-2026-55073: Server-Side Request Forgery (SSRF) (bsc#1279942)