CVE-2025-1240: WinZip 7Z Parsing RCE Vulnerability

CVE-2025-1240 Overview

CVE-2025-1240 is a critical out-of-bounds write vulnerability affecting WinZip's 7Z file parsing functionality. This vulnerability allows remote attackers to execute arbitrary code on affected installations of WinZip. User interaction is required to exploit this vulnerability—the target must visit a malicious page or open a malicious file.

The specific flaw exists within the parsing of 7Z 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.

Critical Impact

Remote code execution via maliciously crafted 7Z archive files, allowing attackers to compromise systems when users open weaponized archives or visit malicious web pages.

Affected Products

• WinZip (versions prior to patched release)
• WinZip applications with 7Z file parsing capabilities
• Systems where WinZip is configured as the default archive handler

Discovery Timeline

• 2025-02-11 - CVE-2025-1240 published to NVD
• 2025-08-18 - Last updated in NVD database

Technical Details for CVE-2025-1240

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption flaw that occurs when an application writes data beyond the boundaries of an allocated memory buffer. In the context of WinZip's 7Z file parsing, the application fails to properly validate user-supplied data within 7Z archive structures before writing to memory.

The attack requires user interaction, meaning victims must either open a malicious 7Z file directly or visit a compromised webpage that triggers the download and processing of a weaponized archive. Once triggered, the vulnerability enables attackers to corrupt memory in a controlled manner, potentially overwriting critical data structures or function pointers to hijack program execution.

Root Cause

The root cause of CVE-2025-1240 lies in insufficient input validation during the parsing of 7Z archive file structures. When WinZip processes a 7Z file, it reads various metadata fields and data blocks that define the archive's contents. The parsing routine fails to adequately verify that size values and data lengths specified within the archive are within expected bounds before performing memory write operations.

This lack of boundary checking allows a specially crafted 7Z file to specify malicious values that cause the parser to write data beyond the allocated buffer's boundaries, corrupting adjacent memory regions.

Attack Vector

The attack vector for this vulnerability is network-based, requiring user interaction. An attacker can deliver the exploit through multiple channels:

1. Email-based attacks: Sending a malicious 7Z archive as an attachment
2. Drive-by downloads: Hosting a weaponized archive on a compromised or malicious website
3. Social engineering: Distributing the malicious file through file-sharing platforms, forums, or messaging applications

When the victim opens the malicious 7Z file with WinZip, the parsing routine processes the crafted data, triggering the out-of-bounds write condition. The attacker can control the write operation to overwrite critical memory structures, ultimately achieving arbitrary code execution in the context of the current user process.

For detailed technical information, refer to the Zero Day Initiative Advisory ZDI-25-047.

Detection Methods for CVE-2025-1240

Indicators of Compromise

• Unusual 7Z files with abnormally large or malformed header structures
• WinZip process crashes or unexpected termination when opening specific archive files
• Memory access violations or application errors logged in Windows Event Viewer related to WinZip
• Suspicious child processes spawned by the WinZip process after opening an archive

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions to monitor for anomalous behavior in WinZip processes, including unexpected memory operations or shellcode execution
• Implement file scanning at email gateways and web proxies to detect malformed 7Z archives before they reach end users
• Configure application whitelisting to prevent unauthorized executables from running if spawned through WinZip exploitation
• Enable Windows Defender Exploit Guard or similar memory protection mechanisms to detect out-of-bounds write attempts

Monitoring Recommendations

• Monitor for unusual parent-child process relationships where winzip.exe spawns unexpected processes such as cmd.exe, powershell.exe, or other scripting interpreters
• Enable detailed logging for file access events involving 7Z archives on sensitive systems
• Track network connections initiated by WinZip processes, as post-exploitation activity may involve command-and-control communication

How to Mitigate CVE-2025-1240

Immediate Actions Required

• Update WinZip to the latest available version that addresses CVE-2025-1240
• Educate users about the risks of opening archive files from untrusted sources
• Implement email filtering rules to quarantine or block 7Z attachments from unknown senders
• Consider temporarily disabling WinZip as the default handler for 7Z files until patching is complete

Patch Information

WinZip has addressed this vulnerability in a security update. Organizations should refer to the Zero Day Initiative Advisory ZDI-25-047 for specific version information and download the latest WinZip release from the official WinZip website. Ensure all endpoints with WinZip installed are updated through your patch management system.

Workarounds

• Use alternative archive utilities for handling 7Z files until WinZip is patched
• Block 7Z file attachments at the email gateway level for organizations that do not require this format
• Implement application sandboxing to isolate WinZip processes and limit the impact of potential exploitation
• Configure Windows Defender Attack Surface Reduction rules to prevent code execution from archive handlers

# Example: Block 7Z attachments at email gateway (adjust for your specific mail server)
# For organizations using Exchange transport rules:
New-TransportRule -Name "Block 7Z Attachments" -AttachmentNameMatchesPatterns "*.7z" -RejectMessageReasonText "7Z attachments are blocked for security reasons"