CVE-2023-31102: 7-Zip Buffer Overflow Vulnerability

CVE-2023-31102 Overview

CVE-2023-31102 is a critical integer underflow vulnerability in 7-Zip's PPMd (Prediction by Partial Matching) decoder implementation within the Ppmd7.c source file. The vulnerability allows attackers to trigger an integer underflow condition followed by an invalid read operation when processing specially crafted 7Z archive files. Successful exploitation could enable an attacker to execute arbitrary code in the context of the current user or cause a denial of service condition.

This vulnerability affects 7-Zip versions prior to 23.00 and impacts enterprise environments that rely on 7-Zip for file compression operations, including systems running NetApp Active IQ Unified Manager and OnCommand Workflow Automation.

Critical Impact

Remote attackers can exploit this vulnerability to execute arbitrary code or cause denial of service by tricking users into opening maliciously crafted 7Z archive files, potentially leading to complete system compromise.

Affected Products

• 7-Zip versions prior to 23.00
• NetApp Active IQ Unified Manager for Windows
• NetApp OnCommand Workflow Automation

Discovery Timeline

• 2023-11-03 - CVE-2023-31102 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-31102

Vulnerability Analysis

The vulnerability resides in the Ppmd7.c file, which implements the PPMd compression algorithm used by 7-Zip for handling 7Z archives. When processing a specially crafted archive, the decoder fails to properly validate input parameters before performing arithmetic operations, resulting in an integer underflow condition.

The flaw occurs during the decompression routine where insufficient bounds checking allows a malicious archive to manipulate internal state variables. When the underflow occurs, subsequent memory read operations access invalid memory locations outside the intended buffer boundaries. This out-of-bounds read can lead to information disclosure or, in combination with other memory corruption techniques, arbitrary code execution.

The attack requires local access to the system and user interaction—specifically, the victim must open a malicious 7Z archive file. However, given the ubiquity of file-sharing scenarios and email attachments, this user interaction requirement is easily satisfied through social engineering vectors.

Root Cause

The root cause is an integer underflow vulnerability (CWE-191) in the PPMd7 decoder implementation. The code fails to properly validate arithmetic operations on size or index values before using them for memory access operations. When a crafted archive provides unexpected values, the subtraction operation wraps around, producing a very large positive value that bypasses subsequent bounds checks and results in invalid memory access.

Attack Vector

The attack vector is local with user interaction required. An attacker must craft a malicious 7Z archive containing specially constructed PPMd-compressed data designed to trigger the integer underflow. The attack scenario involves:

1. Attacker creates a malicious 7Z archive with crafted PPMd compressed content
2. Victim receives the archive via email, download, or file transfer
3. Victim opens or extracts the archive using a vulnerable 7-Zip version
4. The PPMd decoder processes the malicious data, triggering the integer underflow
5. Invalid memory read occurs, potentially leading to code execution or crash

The vulnerability mechanism involves manipulation of internal PPMd decoder state through carefully constructed archive headers and compressed data streams. Technical analysis is available in the DS Security CVE-2023-31102 Analysis and the Zero Day Initiative Advisory ZDI-23-1165.

Detection Methods for CVE-2023-31102

Indicators of Compromise

• Presence of 7-Zip versions prior to 23.00 on endpoints
• 7-Zip process crashes or unexpected termination during archive extraction
• Suspicious 7Z archive files with unusual PPMd-compressed content blocks
• Memory access violations in Ppmd7.c related code paths during archive processing

Detection Strategies

• Deploy endpoint detection rules to identify 7-Zip versions below 23.00 across the enterprise
• Monitor for abnormal process behavior including crashes, high memory consumption, or suspicious child processes spawned by 7-Zip executables
• Implement file inspection capabilities to analyze incoming 7Z archives for malformed PPMd compression headers
• Utilize SentinelOne's behavioral AI to detect exploitation attempts that result in anomalous memory access patterns or code execution

Monitoring Recommendations

• Enable process monitoring for 7z.exe, 7zG.exe, and 7zFM.exe to detect abnormal behavior during archive operations
• Configure alerting for application crashes related to 7-Zip that may indicate exploitation attempts
• Monitor email gateways and file transfer systems for suspicious 7Z archive attachments
• Review endpoint logs for patterns of archive extraction followed by unexpected process activity

How to Mitigate CVE-2023-31102

Immediate Actions Required

• Update 7-Zip to version 23.00 or later immediately from the 7-Zip Official Download Page
• Conduct an enterprise-wide inventory to identify all systems running vulnerable 7-Zip versions
• Implement email gateway filtering to quarantine or scan 7Z attachments before delivery
• Educate users about the risks of opening archive files from untrusted sources

Patch Information

The vulnerability has been addressed in 7-Zip version 23.00 released by the vendor. Organizations should upgrade all instances of 7-Zip to version 23.00 or later. For environments using NetApp products, refer to the NetApp Security Advisory NTAP-20231110-0007 for specific remediation guidance.

Additional discussion and community resources are available on the SourceForge 7-Zip Discussion Thread.

Workarounds

• Restrict 7-Zip usage to trusted archive sources only until patching is complete
• Implement application whitelisting to control which users can execute 7-Zip
• Configure email gateways to block or quarantine 7Z attachments as a temporary measure
• Use alternative archive tools for untrusted files until vulnerable 7-Zip installations are upgraded

# Check installed 7-Zip version on Windows (PowerShell)
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*" | Where-Object { $_.DisplayName -like "*7-Zip*" } | Select-Object DisplayName, DisplayVersion

# Silent upgrade to latest 7-Zip version
# Download 7z2301-x64.msi from official site and run:
msiexec /i 7z2301-x64.msi /qn