CVE-2026-26282

Executive Summary

CVE-2026-26282 is an out-of-bounds heap read vulnerability in the NanaZip file archiver, specifically within its .NET Single File bundle header parser. The flaw exists in versions 5.0.1252.0 through 6.0.1629.0 and is caused by a missing bounds check when parsing crafted archive files. Successful exploitation can lead to application crashes or the unintended leakage of heap memory contents to the user, potentially exposing sensitive data. The vendor has released version 6.0.1630.0 to address this issue.

Supply Chain & Package Security

NanaZip is an open-source file archiver for Windows, distributed via GitHub and potentially through package managers like Chocolatey or Winget. Users should verify the integrity of the downloaded binary using official checksums or signatures. The vulnerability does not directly affect package dependencies but impacts the core parsing logic of the application.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No official vector assigned) Threat Level: Medium (based on impact and exploitability)

While no official CVSS vector is provided, the vulnerability can be characterized as:

• Attack Vector: Local (requires user to open a crafted file)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: Low (heap data leakage)
• Integrity Impact: None
• Availability Impact: Low (crash)

Deep Dive & Mechanics

The vulnerability resides in the .NET Single File bundle header parser within NanaZip. When NanaZip processes a specially crafted archive file, it reads a header that describes the layout of the embedded .NET application. The parser fails to validate the size of the header against the actual data available in the heap buffer. This missing bounds check allows an attacker to craft a file with a header that claims a size larger than the allocated buffer, causing the parser to read beyond the buffer's boundaries.

This out-of-bounds read can result in:

1. Crash: Accessing invalid memory causes a segmentation fault or access violation.
2. Heap Data Leakage: The read data may be displayed to the user (e.g., in a file preview or error message), leaking sensitive information from the heap, such as encryption keys, passwords, or other application data.

The vulnerability is triggered during the parsing of the .NET Single File bundle, which is a format used to package .NET applications into a single executable. NanaZip's support for this format is the attack surface.

Vulnerable vs. Patched Code

The vulnerable code is in the .NET Single File bundle header parser. The missing bounds check is the core issue.

Vulnerable Code (Conceptual):

// Vulnerable: No bounds check on header size
void ParseDotNetSingleFileHeader(char* buffer, size_t bufferSize) {
    DotNetHeader* header = (DotNetHeader*)buffer;
    // Directly uses header->dataSize without checking if it fits in buffer
    char* data = buffer + sizeof(DotNetHeader);
    // Reads header->dataSize bytes from data, potentially out-of-bounds
    ProcessData(data, header->dataSize);
}

Patched Code (Conceptual):

// Patched: Added bounds check
void ParseDotNetSingleFileHeader(char* buffer, size_t bufferSize) {
    DotNetHeader* header = (DotNetHeader*)buffer;
    size_t headerSize = sizeof(DotNetHeader);
    if (headerSize + header->dataSize > bufferSize) {
        // Error: header size exceeds buffer
        return;
    }
    char* data = buffer + headerSize;
    ProcessData(data, header->dataSize);
}

The patch in version 6.0.1630.0 adds a validation check to ensure the claimed header size does not exceed the actual buffer size before reading.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• NanaZip version 5.0.1252.0 to 6.0.1629.0 installed on a Windows target.
• Ability to deliver a crafted archive file to the target (e.g., via email, download).

Steps:

1. Craft the Malicious File: Create a .7z, .zip, or other archive format supported by NanaZip that contains a .NET Single File bundle header with an oversized dataSize field.
2. Deliver the File: Send the crafted archive to the target user via phishing email or social engineering.
3. Trigger the Vulnerability: The user opens the archive with NanaZip. The parser reads the malicious header, causing an out-of-bounds heap read.
4. Observe Outcome: The application may crash, or heap data may be displayed in the user interface (e.g., in a file properties dialog or preview pane).

Note: No public exploit code is available. The above is a conceptual exploitation path.

Blue Team (Defense)

Detection:

• Monitor for crashes of NanaZip.exe with access violation exceptions.
• Look for unusual heap memory patterns in crash dumps.
• Use file integrity monitoring to detect the presence of crafted archives.

Prevention:

• Update NanaZip to version 6.0.1630.0 or later.
• Implement application whitelisting to block untrusted executables.
• Educate users not to open archives from untrusted sources.

Hunting:

• Search for event logs with Event ID 1000 (Application Error) referencing NanaZip.exe.
• Analyze crash dumps for out-of-bounds read patterns.

Indicators of Compromise (IOCs)

• File Hashes: (No specific hashes available; generic crafted archive)
• Process Name: NanaZip.exe
• Event Logs: Application Error (Event ID 1000) with faulting module NanaZip.exe and exception code 0xc0000005 (Access Violation).
• Network: No network indicators (local vulnerability).
• Registry: No known registry modifications.

Detection Engineering

YARA Rule

rule CVE_2026_26282_NanaZip_OOB_Read {
    meta:
        description = "Detects crafted archives exploiting CVE-2026-26282 in NanaZip"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-26282"
    strings:
        $dotnet_magic = { 4D 5A 90 00 }  // MZ header (PE)
        $single_file_magic = { 53 46 42 48 }  // "SFBH" (Single File Bundle Header)
    condition:
        $dotnet_magic at 0 and $single_file_magic and filesize < 10MB
}

Sigma Rule

title: NanaZip Crash Due to Out-of-Bounds Read
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects crashes of NanaZip.exe caused by CVE-2026-26282
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        Provider_Name: 'Application Error'
        Faulting_Module: 'NanaZip.exe'
        Exception_Code: '0xc0000005'
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-26282 NanaZip Crafted Archive Download"; flow:to_server,established; content:"|4d 5a 90 00|"; offset:0; depth:4; content:"|53 46 42 48|"; distance:0; within:4; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

• Upgrade NanaZip to version 6.0.1630.0 or later.
• If upgrade is not possible, avoid opening archives from untrusted sources.

Long-term:

• Implement input validation in all file parsers.
• Use memory-safe languages or bounds-checking libraries.
• Conduct regular security audits of parsing code.

Workaround:

• Disable the .NET Single File bundle parser if possible (not a standard configuration option).

Valters IT
Securing Digital Frontiers