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CVE-2023-45139: XXE Vulnerability in fontTools Python Library

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Overview

The vulnerability, CVE-2023-45139, pertains to an issue in the popular Python library, fontTools. This is used widely for manipulating fonts and has a significant user base across many sectors. The vulnerability, specifically an XML External Entity (XXE) Injection, exists within the library’s subsetting module. This could potentially lead to system compromise or data leakage if exploited, causing significant security concerns for users of the affected version of the library.

Vulnerability Summary

CVE ID: CVE-2023-45139
Severity: High (7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

fontTools Python Library | Versions before 4.43.0

How the Exploit Works

The vulnerability exploits a flaw in the subsetting module of fontTools. Specifically, the module fails to properly handle XML entities within SVG tables of OT-SVG fonts. As a result, an attacker can manipulate these entities to include arbitrary files from the file system or make web requests from the host system. This could lead to unauthorized access to sensitive data or system compromise.

Conceptual Example Code

The following conceptual example shows how an attacker might exploit this vulnerability:

# Import the vulnerable library
import fontTools
# Load a malicious OT-SVG font with an XML entity pointing to a sensitive file
malicious_font = fontTools.ttLib.TTFont("/path/to/malicious_font.otf")
# Parse the font, triggering the vulnerability
malicious_font.parse()

In this example, the “malicious_font.otf” file contains an SVG table with an XML entity that points to a sensitive file or a remote server. When the `parse()` function is called, the XML entity is resolved, leading to a potential data leak or system compromise.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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