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CVE-2025-55780: Null Pointer Dereference Vulnerability in MuPDF

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Overview

CVE-2025-55780 is a significant vulnerability found in MuPDF 1.26.4, a popular software tool for rendering EPUB documents. This vulnerability can lead to a system crash, potentially compromising the system or leading to data leakage. Due to the widespread use of this software, this vulnerability presents a severe threat to numerous organizations and individuals worldwide.

Vulnerability Summary

CVE ID: CVE-2025-55780
Severity: High (7.5/10)
Attack Vector: Remote
Privileges Required: None
User Interaction: Required
Impact: System crash, potential system compromise, and data leakage

Affected Products

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Product | Affected Versions

MuPDF | 1.26.4

How the Exploit Works

The exploit occurs when MuPDF attempts to render a malformed EPUB document. During this process, a null pointer dereference occurs in the function break_word_for_overflow_wrap(). The function calls fz_html_split_flow() to split a FLOW_WORD node, but does not check if node->next is valid before accessing node->next->overflow_wrap. If the split fails or returns a partial node chain, it results in a system crash.

Conceptual Example Code

Here is a conceptual example of how the vulnerability can be exploited using a malformed EPUB file:

<!DOCTYPE html>
<html>
<head>
<title>Malformed EPUB</title>
</head>
<body>
<p>
<!-- Insert malformed FLOW_WORD node here -->
<span style="overflow-wrap: break-word;">...</span>
</p>
</body>
</html>

In the above example, the ‘…’ can be replaced with a specifically crafted string that triggers the null pointer dereference vulnerability when MuPDF attempts to split the FLOW_WORD node.

Mitigation Guidance

Users of MuPDF 1.26.4 are advised to apply the vendor’s patch to fix this vulnerability. Alternatively, a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can be used as temporary mitigation.

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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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