CVE-2025-53816: 7-Zip RAR5 Handler DOS Vulnerability

CVE-2025-53816 Overview

CVE-2025-53816 is a heap buffer overflow vulnerability in 7-Zip, a widely used open-source file archiver known for its high compression ratio. The vulnerability exists in the RAR5 handler where zeroes are written outside the heap buffer boundaries, leading to memory corruption and potential denial of service conditions.

Critical Impact

Exploitation of this vulnerability can cause memory corruption and denial of service in 7-Zip when processing maliciously crafted RAR5 archives, potentially disrupting file extraction operations and system stability.

Affected Products

• 7-Zip versions prior to 25.0.0
• All platforms running vulnerable 7-Zip versions (Windows, Linux, macOS)
• Applications and scripts that integrate 7-Zip for archive handling

Discovery Timeline

• 2025-07-17 - CVE-2025-53816 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-53816

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), a memory corruption flaw that occurs when data is written beyond the allocated boundaries of a heap buffer. In the context of 7-Zip's RAR5 handler, the vulnerability manifests when processing specially crafted RAR5 archives, where zero values are written outside the designated heap buffer region.

The RAR5 format handler in 7-Zip fails to properly validate buffer boundaries during decompression operations. When processing malformed archive data, the handler can write zero bytes past the end of the allocated heap buffer, corrupting adjacent memory structures. This out-of-bounds write can destabilize the application, leading to crashes and denial of service.

The attack requires local access, meaning an attacker must either have local system access or trick a user into opening a malicious RAR5 archive file. While no remote code execution has been confirmed, the memory corruption could potentially be leveraged for more severe attacks depending on the memory layout and heap state.

Root Cause

The root cause of CVE-2025-53816 lies in insufficient bounds checking within the RAR5 decompression handler. When processing compressed data streams, the handler writes decompressed output to a heap-allocated buffer without adequately verifying that the write operations stay within the buffer's allocated size. This allows zero bytes to be written beyond the buffer boundary, corrupting heap metadata or adjacent data structures.

Attack Vector

The attack vector for this vulnerability is local, requiring user interaction to trigger the flaw. An attacker could craft a malicious RAR5 archive file and distribute it through various means such as email attachments, file sharing platforms, or compromised download sites. When a victim attempts to extract or preview the archive using a vulnerable version of 7-Zip, the heap buffer overflow is triggered.

The vulnerability can be exploited through the following scenarios:

The attack requires delivering a specially crafted RAR5 archive to the target system and having the user open it with 7-Zip. Upon parsing the malformed archive structure, the RAR5 handler allocates a heap buffer for decompression but miscalculates the required size or fails to check boundaries during write operations. This results in zero bytes being written outside the allocated buffer, corrupting heap memory and causing the application to crash or behave unpredictably. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-53816

Indicators of Compromise

• Unexpected 7-Zip application crashes when processing RAR5 archives
• System instability or memory-related errors following archive extraction attempts
• Presence of unusually structured or malformed .rar files in user download directories
• Application event logs showing heap corruption or access violation errors from 7-Zip processes

Detection Strategies

• Monitor for abnormal termination of 7z.exe, 7zFM.exe, or 7zG.exe processes with memory-related exit codes
• Implement file inspection rules to detect malformed RAR5 archive structures before user access
• Deploy endpoint detection to identify suspicious RAR files with anomalous header or compression parameters
• Use behavioral analysis to flag repeated 7-Zip crashes within short time periods

Monitoring Recommendations

• Enable application crash logging and forward 7-Zip related events to SIEM platforms
• Configure endpoint protection to alert on heap corruption indicators in archive utilities
• Establish baseline behavior for archive handling processes to detect anomalies
• Review file download and email attachment logs for suspicious RAR5 file sources

How to Mitigate CVE-2025-53816

Immediate Actions Required

• Upgrade 7-Zip to version 25.0.0 or later on all affected systems immediately
• Audit enterprise deployments to identify all instances of vulnerable 7-Zip versions
• Educate users about the risks of opening archive files from untrusted sources
• Consider temporarily restricting RAR5 file handling until patching is complete

Patch Information

7-Zip version 25.0.0 contains the official fix for this vulnerability. The patch addresses the heap buffer overflow by implementing proper bounds checking in the RAR5 decompression handler, ensuring that write operations cannot exceed allocated buffer sizes.

Organizations should download the patched version directly from the official 7-Zip website or trusted distribution channels. For additional context, review the Openwall OSS-Security disclosure and the GitHub Security Advisory.

Workarounds

• Use alternative archive utilities for RAR5 file extraction until 7-Zip can be updated
• Implement email gateway filtering to quarantine RAR5 attachments from external sources
• Deploy application control policies to restrict execution of vulnerable 7-Zip versions
• Configure file system access controls to prevent unauthorized archive extraction in sensitive directories

# Verify 7-Zip version on Windows systems
7z.exe | findstr /i "version"

# Check installed version on Linux
7z | grep -i "version"

# Recommended: Update to patched version 25.0.0 or later
# Download from official 7-Zip sources only