CVE-2023-40481: 7-Zip SquashFS RCE Vulnerability

CVE-2023-40481 Overview

CVE-2023-40481 is a critical out-of-bounds write vulnerability affecting 7-Zip's SquashFS file parsing functionality. This vulnerability allows remote attackers to execute arbitrary code on affected installations of 7-Zip. User interaction is required to exploit this vulnerability, specifically the target must visit a malicious page or open a malicious file.

The specific flaw exists within the parsing of SQFS files. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. This vulnerability was tracked as ZDI-CAN-18589 by the Zero Day Initiative.

Critical Impact

Successful exploitation enables remote code execution in the context of the current process, potentially allowing attackers to gain full control over affected systems through crafted SquashFS archive files.

Affected Products

• 7-Zip version 22.01
• 7-Zip installations processing SquashFS (SQFS) files
• Systems where users may open untrusted archive files

Discovery Timeline

• 2024-05-03 - CVE-2023-40481 published to NVD
• 2025-08-12 - Last updated in NVD database

Technical Details for CVE-2023-40481

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption flaw that occurs when software writes data past the end of an allocated memory buffer. In the context of 7-Zip, this flaw manifests during the parsing of SquashFS archive files, which are commonly used in Linux distributions for read-only compressed filesystems.

The vulnerability requires local access, meaning an attacker must convince a user to open a malicious file or visit a webpage containing a crafted SquashFS archive. Once triggered, the out-of-bounds write can corrupt adjacent memory, potentially allowing the attacker to hijack control flow and execute arbitrary code with the privileges of the 7-Zip process.

Root Cause

The root cause of CVE-2023-40481 lies in insufficient validation of user-supplied data within the SQFS file parsing routines. When 7-Zip processes a SquashFS archive, it reads metadata and data structures from the file without adequately verifying that the sizes and offsets specified in the file are within expected bounds. This allows a specially crafted archive to trigger a write operation that exceeds the boundaries of an allocated buffer.

The lack of boundary checking in the parsing code creates an exploitable condition where malformed SQFS headers or data blocks can cause memory corruption beyond the intended storage region.

Attack Vector

The attack vector for this vulnerability requires user interaction. An attacker would typically:

1. Craft a malicious SquashFS archive file with manipulated metadata designed to trigger the out-of-bounds write condition
2. Distribute the malicious file through phishing emails, compromised websites, or other social engineering techniques
3. Convince the victim to open the file using 7-Zip, either by double-clicking or extracting through the application
4. Upon parsing the malformed SQFS data, the buffer overflow occurs, allowing code execution in the context of the current user

The vulnerability can be delivered through web-based attacks where a user visits a malicious page that prompts download and opening of the crafted archive. For technical details on the exploitation mechanism, refer to the Zero Day Initiative Advisory ZDI-23-1164.

Detection Methods for CVE-2023-40481

Indicators of Compromise

• Unexpected crashes or abnormal behavior in 7-Zip processes when handling .sqfs or SquashFS archives
• Memory access violations or segmentation faults in 7-Zip application logs
• Suspicious SquashFS files with malformed headers or unusually large metadata values
• Child processes spawned by 7-Zip that execute unexpected commands or binaries

Detection Strategies

• Monitor for abnormal 7-Zip process behavior including unexpected memory consumption or process crashes
• Implement endpoint detection rules to identify 7-Zip processes spawning suspicious child processes
• Deploy file integrity monitoring on critical systems to detect unauthorized modifications following exploitation
• Use application whitelisting to prevent execution of unauthorized code from compromised 7-Zip processes

Monitoring Recommendations

• Enable detailed application logging for 7-Zip and archive handling operations
• Configure endpoint protection to alert on memory corruption attempts and out-of-bounds write detections
• Monitor network traffic for downloads of suspicious .sqfs files from untrusted sources
• Implement user behavior analytics to detect unusual file handling patterns

How to Mitigate CVE-2023-40481

Immediate Actions Required

• Update 7-Zip to the latest available version that addresses this vulnerability
• Educate users about the risks of opening archive files from untrusted sources
• Consider blocking or quarantining SquashFS files at email gateways and web proxies until patching is complete
• Review and restrict which users have 7-Zip installed if not operationally required

Patch Information

7-Zip users should upgrade to a version released after the vulnerability was disclosed. Consult the SourceForge Discussion Thread for official vendor communications regarding patches and updates. The Zero Day Initiative Advisory ZDI-23-1164 provides additional technical details and coordinated disclosure information.

Workarounds

• Avoid opening SquashFS archive files from untrusted or unknown sources
• Use alternative archive utilities that are not affected by this vulnerability for handling SQFS files
• Implement application sandboxing or containerization to limit the impact of potential exploitation
• Configure endpoint protection policies to scan and quarantine archive files before user access

# Verify installed 7-Zip version on Windows
# Open Command Prompt and run:
"C:\Program Files\7-Zip\7z.exe" --help | findstr "7-Zip"

# On Linux, check version with:
7z --help | head -2

# Consider using package manager to update:
# Debian/Ubuntu: sudo apt update && sudo apt upgrade p7zip-full
# Windows: Download latest from https://www.7-zip.org/