CVE-2026-44215

Executive Summary

CVE-2026-44215 is a heap-based out-of-bounds write vulnerability in NanaZip, an open-source file archiver. The flaw resides in the UFS/UFS2 filesystem image parser, affecting versions from 5.0.1252.0 up to (but not including) 6.0.1698.0. An attacker can craft a malicious UFS filesystem image that, when opened by a user, triggers a one-byte null write at a controlled offset within a ~254-byte window past the heap allocation boundary. This can lead to application instability or potential code execution, depending on heap layout. The vulnerability has been patched in version 6.0.1698.0.

Supply Chain & Package Security

NanaZip is distributed via GitHub and Microsoft Store. Users should update to the latest version from official sources. No supply chain compromise has been reported.

CVSS Breakdown & Threat Level

• CVSS Score: 4.4 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L
• Attack Vector: Local (AV:L) – requires the victim to open a malicious file.
• Attack Complexity: Low (AC:L) – no special conditions needed.
• Privileges Required: None (PR:N) – no authentication needed.
• User Interaction: Required (UI:R) – victim must open the crafted file.
• Scope: Unchanged (S:U) – vulnerability does not cross trust boundaries.
• Confidentiality Impact: None (C:N) – no data disclosure.
• Integrity Impact: Low (I:L) – limited modification possible.
• Availability Impact: Low (A:L) – may cause crash or instability.

Threat Level: Medium. Exploitation requires user interaction and local access, but the controlled write past heap boundary could be leveraged for more severe impacts in specific heap configurations.

Deep Dive & Mechanics

The vulnerability is a one-byte heap out-of-bounds null write in the UFS/UFS2 filesystem image parser. When NanaZip processes a crafted UFS image, it fails to properly validate the size of a buffer before writing a null byte. The attacker controls the byte offset of the write within a ~254-byte window past the heap allocation boundary.

Root Cause: Insufficient bounds checking in the UFS parser code. The parser likely calculates an offset based on data from the image file without verifying that the offset is within the allocated buffer. This allows writing a null byte at an attacker-controlled position relative to the buffer.

Impact: A null byte write can corrupt heap metadata or adjacent objects. This can lead to:

• Application crash (denial of service).
• Potential code execution if the null byte overwrites a critical pointer or function table entry.

Attack Vector: The attacker must convince a user to open a malicious UFS filesystem image using NanaZip. This could be delivered via email, download, or other means.

Vulnerable vs. Patched Code

The exact code diff is not publicly available, but the fix likely involves adding a bounds check before the write operation.

Vulnerable Code (Conceptual):

void parse_ufs_image(uint8_t *buffer, size_t size, uint32_t offset) {
    // No bounds check on offset
    buffer[offset] = 0; // One-byte null write
}

Patched Code (Conceptual):

void parse_ufs_image(uint8_t *buffer, size_t size, uint32_t offset) {
    if (offset >= size) {
        // Handle error
        return;
    }
    buffer[offset] = 0;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• NanaZip version 5.0.1252.0 to 6.0.1698.0.
• Ability to craft a malicious UFS filesystem image.

Exploitation Steps:

1. Craft Malicious UFS Image: Create a UFS filesystem image with manipulated metadata that causes the parser to write a null byte at a controlled offset past the heap buffer.
2. Deliver Payload: Send the crafted image to the victim via email, download link, or other means.
3. Trigger Vulnerability: Victim opens the image with NanaZip.
4. Achieve Impact: The null write corrupts heap metadata or adjacent objects, potentially leading to code execution or denial of service.

Note: No public exploit code is available. This is a theoretical exploitation path.

Blue Team

Detection:

• Monitor for crashes or unusual behavior in NanaZip when processing UFS images.
• Use file integrity monitoring to detect unexpected modifications to NanaZip binaries.
• Deploy endpoint detection and response (EDR) solutions to detect heap corruption attempts.

Prevention:

• Update NanaZip to version 6.0.1698.0 or later.
• Restrict execution of NanaZip in sensitive environments.
• Educate users not to open untrusted UFS images.

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available.
• Network Indicators: None – vulnerability is local.
• Behavioral Indicators:
  • NanaZip crashes when opening a UFS image.
  • Heap corruption errors in system logs.
  • Unexpected null byte writes in heap memory.

Detection Engineering

YARA Rule

rule CVE_2026_44215_NanaZip_UFS_Heap_Write {
    meta:
        description = "Detects crafted UFS images targeting CVE-2026-44215"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-44215"
    strings:
        $ufs_magic = { 53 54 52 45 41 4D 53 20 } // "STREAMS " or similar UFS magic
        $suspicious_offset = { FF FF FF FF } // Example pattern for large offset
    condition:
        $ufs_magic and $suspicious_offset
}

Sigma Rule

title: NanaZip UFS Heap Out-of-Bounds Write
id: cve-2026-44215
status: experimental
description: Detects potential exploitation of CVE-2026-44215 via NanaZip crashes
author: Valters IT
logsource:
    category: application
    product: nana_zip
detection:
    selection:
        EventID: 1000 // Application crash
        Image: '*\\NanaZip.exe'
        ExceptionCode: '0xc0000005' // Access violation
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-44215 NanaZip UFS Heap Write Attempt"; flow:to_server; content:"|53 54 52 45 41 4D 53 20|"; offset:0; depth:8; content:"|FF FF FF FF|"; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

• Update NanaZip to version 6.0.1698.0 or later.
• Verify the update via official GitHub repository or Microsoft Store.

Long-term:

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

Workarounds:

• Avoid opening UFS files from untrusted sources.
• Use alternative archive tools for UFS images until patched.

Valters IT