Summary
WeasyPrint crashes with a segmentation fault (SIGSEGV, signal 11) when using @font-face to override certain CSS generic font-family names (monospace, serif). The original .html file triggering the crash was generated using sphinx -b simplepdf, which in turn uses weasyprint. Here is a minimal reproduction. weasyprint is installed on a linux testing system using:
uv tool install weasyprint
uv tool list
sphinx v9.1.0
- sphinx-apidoc
- sphinx-autogen
- sphinx-build
- sphinx-quickstart
sphinx-autobuild v2025.8.25
- sphinx-autobuild
twill v3.3.1
- twill
- twill-fork
weasyprint v68.1
- weasyprint
The bug does not seem to be font-file specific - any TTF/OTF font triggers the crash when used with these generic names.
Environment
System: Linux
Machine: x86_64
Version: #1 SMP PREEMPT_DYNAMIC Debian 6.18.5-1 (2026-01-16)
Release: 6.18.5+deb14-amd64
WeasyPrint version: 68.1
Python version: 3.13.12
Pydyf version: 0.12.1
Pango version: 15700
Minimal Reproduction
Crashes (exit code 139):
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>WeasyPrint Crash - Minimal Reproduction</title>
<style>
/* BUG: Using generic font-family name "monospace" in @font-face crashes weasyprint */
@font-face {
font-family: monospace;
src: url(fonts/FiraMono-Regular.ttf);
}
pre { font-family: monospace; }
</style>
</head>
<body>
<pre>Hello World</pre>
</body>
</html>Works (exit code 0):
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>WeasyPrint Works - Minimal Reproduction</title>
<style>
/* WORKS: Using custom font-family name instead of generic "monospace" */
@font-face {
font-family: my-mono;
src: url(fonts/FiraMono-Regular.ttf);
}
pre { font-family: my-mono; }
</style>
</head>
<body>
<pre>Hello World</pre>
</body>
</html>Steps to Reproduce
# This CRASHES (exit code 139)
weasyprint test_crash.html output.pdf
# This WORKS (exit code 0)
weasyprint test_works.html output.pdf
The only difference between the two files is:
test_crash.html: font-family: monospacetest_works.html: font-family: my-mono
Summary
WeasyPrint crashes with a segmentation fault (SIGSEGV, signal 11) when using
@font-faceto override certain CSS generic font-family names (monospace,serif). The original .html file triggering the crash was generated using sphinx -b simplepdf, which in turn uses weasyprint. Here is a minimal reproduction. weasyprint is installed on a linux testing system using:The bug does not seem to be font-file specific - any TTF/OTF font triggers the crash when used with these generic names.
Environment
Minimal Reproduction
Crashes (exit code 139):
Works (exit code 0):
Steps to Reproduce
The only difference between the two files is:
test_crash.html:font-family: monospacetest_works.html:font-family: my-mono