NULL Pointer Dereference in NanaZip Archive Extraction

Executive Summary

CVE-2026-55783 is a NULL pointer dereference vulnerability in NanaZip's seven custom archive handlers. The issue occurs in the Extract() function when processing the entire archive, as the handlers unconditionally dereference the caller-supplied Indices array even when it is NULL (indicating "extract everything").

This leads to an access violation crash when the archive engine passes Indices=NULL and NumItems=0xFFFFFFFF, as the handlers incorrectly use the raw Indices[i] value instead of the computed ActualFileIndex for the GetStream call.

The vulnerability affects NanaZip versions 6.5 Preview (6.5.1742.0) and earlier and is fixed in version 6.5.1749.0 by using the correct ActualFileIndex in all affected handlers.

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Impact Analysis

This vulnerability can cause a denial of service by crashing the NanaZip process when a maliciously crafted archive file is opened and extracted.

The impact is limited to availability loss only, meaning the software may crash but no data corruption or unauthorized access is indicated.

Exploitation requires user interaction, such as opening or extracting a specially crafted archive file.

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Detection Guidance

This vulnerability causes a NULL pointer dereference leading to a process crash when extracting certain archive files with vulnerable NanaZip versions. Detection can involve monitoring for unexpected crashes or denial of service events related to NanaZip when handling archive extraction.

Since the issue occurs when the Extract function is called with Indices=NULL and NumItems=0xFFFFFFFF, testing extraction of suspicious or untrusted archive files using NanaZip versions prior to 6.5.1749.0 can help identify the vulnerability.

There are no specific commands provided in the resources, but you can monitor NanaZip process crashes in system logs or use debugging tools to trace crashes during archive extraction.

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Compliance Impact

This vulnerability causes a NULL pointer dereference leading to a process crash, which results in a denial of service condition. It does not involve unauthorized access to sensitive data or data breaches.

Since the impact is limited to availability loss only and requires user interaction, it has a low severity score and does not directly affect confidentiality or integrity of data.

Therefore, this vulnerability is unlikely to have a direct impact on compliance with common standards and regulations such as GDPR or HIPAA, which primarily focus on protecting personal data confidentiality, integrity, and privacy.

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Mitigation Strategies

The immediate mitigation step is to update NanaZip to version 6.5.1749.0 or later, where the vulnerability is fixed by correctly passing the ActualFileIndex in the Extract function.

Until the update is applied, avoid extracting untrusted or suspicious archive files with vulnerable versions of NanaZip to prevent denial of service crashes.

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