CVE-2023-20032: Cisco Secure Endpoint RCE Vulnerability

CVE-2023-20032 Overview

CVE-2023-20032 is a critical heap buffer overflow vulnerability discovered in the HFS+ partition file parser of the ClamAV scanning library. This vulnerability allows an unauthenticated, remote attacker to execute arbitrary code on affected systems by submitting a specially crafted HFS+ partition file to be scanned.

The vulnerability stems from a missing buffer size check during the parsing of HFS+ partition files, which can result in a heap buffer overflow write. A successful exploit allows attackers to execute arbitrary code with the privileges of the ClamAV scanning process or crash the process, resulting in a denial of service (DoS) condition.

Critical Impact

Remote attackers can achieve arbitrary code execution with ClamAV process privileges without authentication, potentially compromising the entire scanning infrastructure and any systems relying on ClamAV for malware protection.

Affected Products

• ClamAV versions 1.0.0 and earlier (including 1.0.0-rc and 1.0.0-rc2)
• ClamAV versions 0.105.1 and earlier
• ClamAV versions 0.103.7 and earlier
• Cisco Secure Endpoint (Linux, macOS, Windows)
• Cisco Secure Endpoint Private Cloud
• Cisco Web Security Appliance
• Stormshield Network Security

Discovery Timeline

• February 15, 2023 - Vulnerability disclosed via ClamAV blog
• March 1, 2023 - CVE-2023-20032 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20032

Vulnerability Analysis

This vulnerability exists within the HFS+ partition file parser component of ClamAV. HFS+ (Hierarchical File System Plus) is Apple's proprietary file system used in macOS. ClamAV includes parsing capabilities for various file formats, including HFS+ partition files, to enable comprehensive malware scanning.

The core issue lies in the absence of proper bounds checking when processing HFS+ partition data structures. When ClamAV parses a maliciously crafted HFS+ file, the parser fails to validate the size of input data before writing it to a heap-allocated buffer. This missing validation allows an attacker to overflow the allocated buffer, corrupting adjacent heap memory.

The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input) and CWE-787 (Out-of-bounds Write), both of which are common memory corruption weaknesses that frequently lead to code execution vulnerabilities.

Root Cause

The root cause of CVE-2023-20032 is a missing buffer size check in the HFS+ partition file parsing code. When the ClamAV engine processes an HFS+ partition file, it allocates a heap buffer to store parsed data. However, the code fails to verify that the incoming data size does not exceed the allocated buffer capacity before performing the write operation.

This oversight allows crafted input data to exceed buffer boundaries, leading to heap corruption. The lack of input validation is a fundamental secure coding violation that enables attackers to manipulate memory layouts for exploitation purposes.

Attack Vector

The attack vector for this vulnerability is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability through the following methods:

1. Email Attachment Scanning: Submitting a malicious HFS+ partition file as an email attachment to a mail server protected by ClamAV
2. Web Gateway Scanning: Uploading a crafted file through web applications where ClamAV performs content inspection
3. File Share Scanning: Placing malicious files on network shares monitored by ClamAV
4. Direct API Submission: Sending crafted files directly to ClamAV scanning interfaces

Upon successful exploitation, the attacker gains code execution with the same privileges as the ClamAV scanning process. In many enterprise deployments, this process runs with elevated privileges to access files across the system, potentially leading to full system compromise.

The exploitation mechanism involves crafting an HFS+ partition file with malformed metadata structures that trigger the buffer overflow during parsing. The attacker carefully controls the overflow data to overwrite critical heap structures or function pointers, redirecting execution flow to attacker-controlled code.

Detection Methods for CVE-2023-20032

Indicators of Compromise

• Unexpected crashes or restarts of clamd or clamscan processes
• Presence of unusual HFS+ partition files (.hfs, .dmg) in scan directories or email attachments
• Memory corruption errors in ClamAV log files
• Anomalous process spawning from ClamAV parent processes

Detection Strategies

• Monitor ClamAV process behavior for signs of exploitation such as unexpected child process creation
• Implement file type filtering to log or quarantine HFS+ partition files before ClamAV processing
• Deploy memory protection technologies (ASLR, DEP) and monitor for bypass attempts
• Use network intrusion detection to identify large or malformed HFS+ files in transit

Monitoring Recommendations

• Enable verbose logging for ClamAV scanning operations and review logs for parsing errors
• Configure SIEM alerts for ClamAV process crashes or abnormal termination patterns
• Monitor system calls from ClamAV processes for suspicious activity such as shell spawning
• Track file uploads and email attachments containing Apple disk image formats

How to Mitigate CVE-2023-20032

Immediate Actions Required

• Update ClamAV to version 0.103.8, 0.105.2, or 1.0.1 or later immediately
• Update Cisco Secure Endpoint to the latest patched version for your platform
• Apply Cisco Web Security Appliance security updates as specified in the vendor advisory
• Review and restrict file types allowed through scanning gateways if patching is delayed

Patch Information

Cisco has released security updates addressing this vulnerability. Administrators should apply the following patches:

• ClamAV: Upgrade to versions 0.103.8, 0.105.2, or 1.0.1 or later
• Cisco Secure Endpoint: Apply the latest security updates for Linux, macOS, and Windows platforms
• Cisco Secure Endpoint Private Cloud: Update to the latest patched release
• Cisco Web Security Appliance: Apply vendor-provided security patches

For detailed patch information and download links, refer to the Cisco Security Advisory.

Workarounds

• Disable HFS+ file parsing in ClamAV configuration if Apple file system scanning is not required for your environment
• Implement network-level filtering to block or quarantine HFS+ partition files before they reach ClamAV
• Deploy ClamAV in isolated containers or sandboxed environments to limit the impact of potential exploitation
• Use application allowlisting to prevent unauthorized code execution from ClamAV process context

# Configuration example - Disable HFS+ scanning in clamd.conf (temporary workaround)
# Add the following to your clamd.conf or freshclam.conf
# Note: This reduces scanning coverage and should only be used until patching is complete

# Scan archive files
ScanArchive yes

# If available in your ClamAV version, disable specific parsers
# Consult ClamAV documentation for parser-specific options

# Restart ClamAV service after configuration changes
# systemctl restart clamav-daemon