CVE-2021-21236

CairoSVG is a Python (pypi) package. CairoSVG is an SVG converter based on Cairo. In CairoSVG before version 2.5.1, there is a regular expression denial of service (REDoS) vulnerability. When processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time. This is fixed in version 2.5.1. See Referenced GitHub advisory for more information.

Doyensec Vulnerability Advisory

• Regular Expression Denial of Service (REDoS) in cairosvg
• Affected Product: CairoSVG v2.0.0+
• Vendor: https://github.com/Kozea
• Severity: Medium
• Vulnerability Class: Denial of Service
• Author(s): Ben Caller (Doyensec)

Summary

When processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time.

Technical description

The vulnerable regular expressions are

https://github.com/Kozea/CairoSVG/blob/9c4a982b9a021280ad90e89707eacc1d114e4ac4/cairosvg/colors.py#L190-L191

The section between 'rgb(' and the final ')' contains multiple overlapping groups.

Since all three infinitely repeating groups accept spaces, a long string of spaces causes catastrophic backtracking when it is not followed by a closing parenthesis.

The complexity is cubic, so doubling the length of the malicious string of spaces makes processing take 8 times as long.

Reproduction steps

Create a malicious SVG of the form:

<svg width="1" height="1"><rect fill="rgb(                     ;"/></svg>

with the following code:

'<svg width="1" height="1"><rect fill="rgb(' + (' ' * 3456) + ';"/></svg>'

Note that there is no closing parenthesis before the semi-colon.

Run cairosvg e.g.:

cairosvg cairo-redos.svg -o x.png

and notice that it hangs at 100% CPU. Increasing the number of spaces increases the processing time with cubic complexity.

Remediation

Fix the regexes to avoid overlapping parts. Perhaps remove the [ \n\r\t]* groups from the regex, and use .strip() on the returned capture group.

Disclosure timeline

• 2020-12-30: Vulnerability disclosed via email to CourtBouillon

CairoSVG is a Python (pypi) package. CairoSVG is an SVG converter based on Cairo. In CairoSVG before version 2.5.1, there is a regular expression denial of service (REDoS) vulnerability. When processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time. This is fixed in version 2.5.1. See Referenced GitHub advisory for more information.

When processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time (CVE-2021-21236).

This update for python-CairoSVG fixes the following issues:

• CVE-2023-27586: Don't allow fetching external files unless explicitly asked for. (boo#1209538)

• Update to version 2.5.2

  • Fix marker path scale

• Update to version 2.5.1 (boo#1180648, CVE-2021-21236):

  • Security fix: When processing SVG files, CairoSVG was using two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provided a malicious SVG, it could make CairoSVG get stuck processing the file for a very long time.
  • Fix marker positions for unclosed paths
  • Follow hint when only output_width or output_height is set
  • Handle opacity on raster images
  • Don’t crash when use tags reference unknown tags
  • Take care of the next letter when A/a is replaced by l
  • Fix misalignment in node.vertices

• Updates for version 2.5.0.

  • Drop support of Python 3.5, add support of Python 3.9.
  • Add EPS export
  • Add background-color, negate-colors, and invert-images options
  • Improve support for font weights
  • Fix opacity of patterns and gradients
  • Support auto-start-reverse value for orient
  • Draw images contained in defs
  • Add Exif transposition support
  • Handle dominant-baseline
  • Support transform-origin

This update for python-CairoSVG fixes the following issues:

• CVE-2023-27586: Don't allow fetching external files unless explicitly asked for. (boo#1209538)

• Update to version 2.5.2

  • Fix marker path scale

• Update to version 2.5.1 (boo#1180648, CVE-2021-21236):

  • Security fix: When processing SVG files, CairoSVG was using two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provided a malicious SVG, it could make CairoSVG get stuck processing the file for a very long time.

  • Fix marker positions for unclosed paths

  • Follow hint when only output_width or output_height is set

  • Handle opacity on raster images

  • Don’t crash when use tags reference unknown tags

  • Take care of the next letter when A/a is replaced by l

  • Fix misalignment in node.vertices

• Updates for version 2.5.0.

  • Drop support of Python 3.5, add support of Python 3.9.
  • Add EPS export
  • Add background-color, negate-colors, and invert-images options
  • Improve support for font weights
  • Fix opacity of patterns and gradients
  • Support auto-start-reverse value for orient
  • Draw images contained in defs
  • Add Exif transposition support
  • Handle dominant-baseline
  • Support transform-origin

These are all security issues fixed in the python310-CairoSVG-2.7.1-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python313-CairoSVG-2.9.0-1.3 package on the GA media of openSUSE Tumbleweed.

CairoSVG is a Python (pypi) package. CairoSVG is an SVG converter based on Cairo. In CairoSVG before version 2.5.1, there is a regular expression denial of service (REDoS) vulnerability. When processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS). If an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time. This is fixed in version 2.5.1. See Referenced GitHub advisory for more information.