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Denial of service caused by infinite recursion when parsing SVG images

Moderate severity GitHub Reviewed Published Dec 13, 2023 in dompdf/dompdf • Updated Dec 18, 2023

Package

composer dompdf/dompdf (Composer)

Affected versions

< 2.0.4

Patched versions

2.0.4

Description

Summary

When parsing SVG images Dompdf performs an initial validation to ensure that paths within the SVG are allowed. One of the validations is that the SVG document does not reference itself. However, a recursive chained using two or more SVG documents is not correctly validated. Depending on the system configuration and attack pattern this could exhaust the memory available to the executing process and/or to the server itself.

Details

php-svg-lib, when run in isolation, does not support SVG references for image elements. An SVG document can, however, be referenced and Dompdf will run that reference through the same validation. Dompdf currently includes validation to prevent self-referential image references, but a chained reference is not checked. A malicious actor may thus trigger infinite recursion in the validation process by chaining references between two or more SVG images.

PoC

This following sources can be used to bypass validation provided by Dompdf:

recurse.html

<img src="one.svg">

one.svg

<svg width="200" height="200" xmlns="http://www.w3.org/2000/svg">
  <image href="two.svg" />
</svg>

two.svg

<svg width="200" height="200" xmlns="http://www.w3.org/2000/svg">
  <image href="one.svg" />
</svg>

Impact

When Dompdf parses the above payload, it will crash due after exceeding the allowed execution time or memory usage. An attacker sending multiple request to a system can potentially cause resource exhaustion to the point that the system is unable to handle incoming request.

References

@bsweeney bsweeney published to dompdf/dompdf Dec 13, 2023
Published by the National Vulnerability Database Dec 13, 2023
Published to the GitHub Advisory Database Dec 13, 2023
Reviewed Dec 13, 2023
Last updated Dec 18, 2023

Severity

Moderate
5.3
/ 10

CVSS base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Weaknesses

CVE ID

CVE-2023-50262

GHSA ID

GHSA-3qx2-6f78-w2j2

Source code

Credits

Checking history
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