CVE-2026-27014

Executive Summary

CVE-2026-27014 is a denial-of-service (DoS) vulnerability in NanaZip, an open-source file archiver. The flaw resides in the ROMFS archive parser, affecting versions 5.0.1252.0 through 6.0.1629.0. An attacker can craft a malicious ROMFS archive containing circular NextOffset chains or deeply nested directories, causing an infinite loop or stack overflow when parsed. This leads to application hang or crash, effectively denying service to the user. The vulnerability is patched in NanaZip version 6.0.1630.0. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time.

Supply Chain & Package Security

NanaZip is distributed via GitHub releases and potentially through package managers like Chocolatey or Winget. Users should verify the integrity of downloaded binaries using checksums provided by the official repository. The vulnerability does not affect package registries like NPM, PyPI, Go, or Ruby, but the supply chain risk is present if users obtain NanaZip from unofficial sources.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned. Based on the vulnerability characteristics, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – requires the user to open a malicious archive.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – user must open the file.
• Scope (S): Unchanged (U) – affects only the vulnerable component.
• Confidentiality (C): None (N) – no data breach.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – causes denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium. Exploitation requires user interaction and does not lead to data compromise, but it can disrupt operations.

Deep Dive & Mechanics

The vulnerability exists in the ROMFS (ROM File System) archive parser within NanaZip. ROMFS is a simple read-only filesystem format used for embedded systems and firmware. The parser processes directory entries and file offsets.

Root Cause:

1. Circular NextOffset Chains: The parser iterates through directory entries using a NextOffset field. If a malicious archive creates a circular reference (e.g., entry A points to entry B, which points back to A), the parser enters an infinite loop, consuming CPU resources and hanging the application.
2. Deeply Nested Directories: The parser uses recursion to traverse directory structures. An archive with an excessive nesting depth (e.g., thousands of subdirectories) causes a stack overflow, crashing the application.

Attack Vector: An attacker crafts a specially designed ROMFS archive file and distributes it via email, downloads, or other means. When a user opens the archive with a vulnerable version of NanaZip, the parser triggers the DoS condition.

Impact: The application becomes unresponsive or crashes. The user must terminate the process manually, potentially losing unsaved work. No data is corrupted or exfiltrated.

Vulnerable vs. Patched Code

The patch in version 6.0.1630.0 introduces bounds checking and recursion depth limits.

Vulnerable Code (Conceptual):

// Vulnerable: No loop detection or depth limit
void parse_romfs_directory(offset) {
    while (offset != 0) {
        entry = read_entry(offset);
        if (entry.is_directory) {
            parse_romfs_directory(entry.next_offset); // Recursive call
        }
        offset = entry.next_offset; // No cycle detection
    }
}

Patched Code (Conceptual):

// Patched: Depth limit and cycle detection
#define MAX_DEPTH 100
void parse_romfs_directory(offset, depth) {
    if (depth > MAX_DEPTH) return; // Prevent stack overflow
    visited_offsets = hash_set();
    while (offset != 0) {
        if (visited_offsets.contains(offset)) break; // Cycle detection
        visited_offsets.add(offset);
        entry = read_entry(offset);
        if (entry.is_directory) {
            parse_romfs_directory(entry.next_offset, depth + 1);
        }
        offset = entry.next_offset;
    }
}

Exploitation & Lab Setup

Red Team (Offensive)

Objective: Create a proof-of-concept ROMFS archive that triggers the DoS.

Tools Required:

• Python 3.x with struct module
• NanaZip vulnerable version (e.g., 5.0.1252.0)

Steps:

1. Craft Malicious ROMFS Archive: Use Python to generate a ROMFS file with a circular NextOffset chain.

   import struct
   import os
   
   # Create a minimal ROMFS header
   header = b'\x00' * 16  # Placeholder header
   
   # Create two directory entries that point to each other
   entry1 = struct.pack('<II', 0x10, 0x20)  # next_offset=0x20, spec_data=0x10
   entry2 = struct.pack('<II', 0x20, 0x10)  # next_offset=0x10, spec_data=0x20
   
   # Build the archive
   archive = header + entry1 + entry2
   
   with open('malicious.romfs', 'wb') as f:
       f.write(archive)
   

2. Deliver the Archive: Send the file to the target via email or file sharing.
3. Trigger the Vulnerability: The target opens the archive with NanaZip. The application hangs or crashes.

Expected Outcome: NanaZip becomes unresponsive, requiring termination via Task Manager.

Blue Team (Defensive)

Objective: Detect and block malicious ROMFS archives.

Detection Strategy:

• Monitor for NanaZip crashes or hangs.
• Use file scanning to detect suspicious ROMFS structures.
• Implement application whitelisting to prevent untrusted archives.

Hunting Query (Sysmon):

<EventID>1</EventID>
<Data Name="Image">*NanaZip*</Data>
<Data Name="CommandLine">*.romfs*</Data>

Look for repeated crashes or high CPU usage events.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None publicly available; generate your own for PoC)
• File Names: *.romfs files with unusual size (e.g., very small or large)
• Process Behavior: NanaZip.exe consuming 100% CPU or crashing repeatedly
• Network: No network indicators (local DoS only)
• Registry: No persistence mechanisms

Detection Engineering

YARA Rule

rule CVE_2026_27014_ROMFS_Circular_Chain {
    meta:
        description = "Detects ROMFS archives with circular NextOffset chains"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2026-27014"
    strings:
        $romfs_magic = { 52 4F 4D 46 } // "ROMF" magic bytes
        $circular_pattern = { ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? } // Placeholder
    condition:
        $romfs_magic at 0 and #circular_pattern > 1
}

Sigma Rule

title: NanaZip ROMFS Parser DoS Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2026-27014 via malicious ROMFS archives
author: Valters IT
date: 2025/04/10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\NanaZip.exe'
        CommandLine|contains: '.romfs'
    condition: selection
falsepositives:
    - Legitimate ROMFS archives from trusted sources
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-27014 NanaZip ROMFS DoS Attempt"; flow:to_server,established; content:"ROMF"; depth:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update NanaZip: Upgrade to version 6.0.1630.0 or later from the official GitHub repository.
2. Block Malicious Archives: Use endpoint protection to scan and block suspicious ROMFS files.
3. User Awareness: Educate users not to open archives from untrusted sources.

Long-Term Measures:

• Implement input validation and recursion depth limits in all archive parsers.
• Conduct regular code reviews and fuzz testing on file parsing components.
• Monitor for similar vulnerabilities in other archive formats (e.g., ISO, UDF).

Workaround: If patching is not immediately possible, avoid opening ROMFS archives from untrusted sources. Use alternative archive tools for ROMFS files.

Valters IT
Securing Digital Frontiers