CVE-2025-10101: Avast Antivirus Buffer Overflow Vulnerability

CVE-2025-10101 Overview

CVE-2025-10101 is a critical heap-based buffer overflow and out-of-bounds write vulnerability affecting Avast Antivirus on MacOS. The vulnerability occurs during the processing of specially crafted Mach-O files, which are the native executable format for macOS and iOS systems. When exploited, this vulnerability could allow an attacker to achieve local code execution or cause a denial of service condition that disables antivirus protection on the affected system.

The vulnerability is particularly concerning because it targets security software itself, potentially allowing attackers to neutralize endpoint protection before conducting further malicious activities.

Critical Impact

Successful exploitation could lead to arbitrary code execution with the privileges of the antivirus process or complete disabling of antivirus protection, leaving the system vulnerable to additional attacks.

Affected Products

• Avast Antivirus for MacOS versions from 15.7 before 3.9.2025

Discovery Timeline

• 2025-12-01 - CVE-2025-10101 published to NVD
• 2025-12-02 - Last updated in NVD database

Technical Details for CVE-2025-10101

Vulnerability Analysis

This vulnerability has been classified under CWE-122 (Heap-based Buffer Overflow). The CVSS 3.1 base score is 8.1 (HIGH) with the vector string CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

The scoring breakdown indicates:

• Attack Vector (AV:L): Local access is required to exploit this vulnerability
• Attack Complexity (AC:H): Exploitation requires specific conditions to be met
• Privileges Required (PR:N): No privileges are needed to attempt exploitation
• User Interaction (UI:N): No user interaction is required
• Scope (S:C): The vulnerability can affect resources beyond its security scope
• Impact: High impact on confidentiality, integrity, and availability

The EPSS (Exploit Prediction Scoring System) probability is 0.018%, placing this vulnerability in the 3.945 percentile as of 2025-12-16.

Root Cause

The root cause of CVE-2025-10101 is improper bounds checking during the parsing of Mach-O executable files by the Avast Antivirus scanning engine. Mach-O files contain multiple headers, load commands, and segments that define the executable structure. When the antivirus engine processes a maliciously crafted Mach-O file with manipulated header values or segment sizes, it fails to properly validate these parameters before allocating and writing to heap memory.

This results in a heap-based buffer overflow condition where data is written beyond the allocated buffer boundaries, potentially corrupting adjacent heap memory structures or overwriting critical control data.

Attack Vector

The attack requires local access to the target system. An attacker would need to place a specially crafted Mach-O file on the system where Avast Antivirus would scan it. This could occur through:

1. Email attachment scanning: A malicious Mach-O file attached to an email that triggers automatic scanning
2. Download folder monitoring: Placing the crafted file in a monitored directory
3. Manual scan triggering: Convincing a user to scan a specific directory containing the malicious file
4. Real-time protection: Any file system operation involving the malicious file that triggers the real-time scanner

The attack does not require user interaction beyond normal system operations that would cause the antivirus to scan the malicious file. The crafted Mach-O file would contain malformed load commands or segment definitions with incorrect size fields, triggering the out-of-bounds write condition during parsing.

Detection Methods for CVE-2025-10101

Indicators of Compromise

• Unexpected crashes or restarts of Avast Antivirus processes on MacOS
• Presence of unusual or malformed Mach-O files in scanned directories
• Antivirus service becoming unresponsive or disabled without user action
• Unusual memory consumption by antivirus processes prior to crash
• System logs indicating segmentation faults or memory access violations in Avast components

Detection Strategies

Organizations should implement monitoring for Avast Antivirus process stability on MacOS endpoints. Sudden crashes or service interruptions during file scanning operations could indicate exploitation attempts. Security teams should also monitor for the presence of files with anomalous Mach-O headers that deviate significantly from standard executable formats.

File integrity monitoring solutions can help detect malicious files before they reach the antivirus scanner. Additionally, behavioral analysis tools can identify patterns consistent with heap corruption attacks, such as unexpected memory allocation patterns or process memory anomalies.

Monitoring Recommendations

1. Enable crash reporting and centralized logging for Avast Antivirus processes
2. Monitor MacOS system logs (/var/log/system.log) for antivirus-related crashes
3. Implement alerting for antivirus service interruptions or unexpected restarts
4. Deploy endpoint detection solutions that can identify malformed Mach-O files
5. Track file scanning activity logs for patterns that precede crashes

How to Mitigate CVE-2025-10101

Immediate Actions Required

• Update Avast Antivirus for MacOS to version 3.9.2025 or later immediately
• Verify that automatic updates are enabled for the antivirus software
• Monitor antivirus service health to detect any exploitation attempts
• Review recent scan logs for any anomalous behavior prior to updating
• Consider temporarily restricting file scanning scope to critical areas until patched

Patch Information

Gen Digital (the parent company of Avast) has released a security update that addresses this vulnerability. Users should update their Avast Antivirus installation to version 3.9.2025 or later. The update includes improved input validation for Mach-O file parsing to prevent heap-based buffer overflow conditions.

For official security advisory information, refer to: Gen Digital Security Advisories

Workarounds

If immediate patching is not possible, organizations should consider the following temporary mitigations:

1. Limit scan scope: Configure the antivirus to exclude directories where untrusted Mach-O files may be introduced, though this reduces overall protection
2. Enhanced monitoring: Implement additional monitoring for antivirus service health and restart the service automatically if it crashes
3. Network controls: Strengthen email gateway and web proxy filtering to block potentially malicious Mach-O files before they reach endpoints
4. Layered defense: Ensure additional security controls are in place to compensate for potential antivirus disruption, including EDR solutions like SentinelOne that provide independent protection

Note that these workarounds reduce overall security posture and should only be considered as temporary measures until the official patch can be applied.