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A critical vulnerability has been discovered in the XAR file format parser of ClamAV, an open-source malware detection engine widely used for scanning files, archives, and email attachments. Tracked as CVE-2026-20348, this flaw stems from improper boundary checks when processing content within XAR (XML Archive) files during scanning operations. XAR is a file format commonly used for packaging and distributing software components, making it a frequent target for scanning by antivirus solutions.
The technical root cause lies in inadequate input validation and memory allocation boundary checks within the XAR parser implementation. When the parser encounters a malformed or specially crafted XAR file, it fails to properly validate the length of inputs and memory boundaries, leading to potential buffer overflows or memory corruption conditions. This weakness aligns with CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), CWE-120 (Buffer Copy without Checking Size of Input), and CWE-787 (Out-of-Bounds Write).
An unauthenticated, remote attacker can exploit this vulnerability by submitting a crafted file containing XAR content to a system running a vulnerable version of ClamAV. The attack requires no authentication and can be initiated remotely, making it particularly dangerous in environments where automated scanning occurs across multiple systems. The exploitation is considered easy, and while no public exploit is currently available, the estimated exploit price on underground markets ranges from $5,000 to $25,000.
Successful exploitation causes the ClamAV scanning process to terminate unexpectedly, resulting in a Denial-of-Service (DoS) condition that interrupts malware scanning operations. Because the flaw involves memory corruption arising from improper bounds and size handling, the vulnerability may also present the possibility of impacts beyond process termination, including potential arbitrary code execution. The vulnerability affects ClamAV versions 0.98.1 through 1.5.3 and is fixed in versions 1.4.6 and 1.5.4.
Cisco, the steward of ClamAV, published an advisory on August 7, 2026, warning that this vulnerability affects Cisco Secure Endpoint Connector deployments on Windows, Linux, and macOS. Cisco assigned a high-severity rating to affected Windows deployments and a medium rating to Linux and macOS deployments because of differences in the privileges used by the ClamAV scanning process. The advisory was updated on August 10, 2026, highlighting the availability of public proof-of-concept (PoC) code for related vulnerabilities. Organizations are urged to update to patched versions immediately, as no effective workarounds are currently available.
DailyCVE Form:
Platform: ClamAV, Cisco Secure Endpoint
Version: 0.98.1 – 1.5.3
Vulnerability: Memory Corruption (XAR Parser)
Severity: Critical (CVSS 7.5)
Date: August 7, 2026
Prediction: Patch expected August 2026
What Undercode Say:
Check ClamAV version clamscan --version Check for vulnerable versions (0.98.1 through 1.5.3) clamscan --version | grep -E "ClamAV [bash].[0-5].[0-3]" Verify if the system is running a vulnerable ClamAV instance ps aux | grep clamd Check the ClamAV package version (Debian/Ubuntu) dpkg -l | grep clamav Check the ClamAV package version (RHEL/CentOS) rpm -qa | grep clamav Download and install the patched version 1.5.4 from the official repository wget https://www.clamav.net/downloads/production/clamav-1.5.4.tar.gz tar -xzf clamav-1.5.4.tar.gz cd clamav-1.5.4 ./configure --prefix=/usr/local/clamav make sudo make install Restart the ClamAV daemon after patching sudo systemctl restart clamav-daemon Verify the new version clamscan --version
Exploit: (Educational Purposes!)
Educational demonstration only - Do NOT use maliciously Crafting a malformed XAR file to trigger improper boundary checks This is a conceptual example based on the vulnerability description Create a malformed XAR header with oversized table of contents echo -n "xar!" > malicious.xar Corrupt the table of contents size field (offset 0x10-0x13) printf "\xFF\xFF\xFF\xFF" >> malicious.xar Append garbage data to trigger memory corruption dd if=/dev/urandom of=malicious.xar bs=1 count=1024 seek=20 Submit the crafted file for scanning (example using clamscan) clamscan malicious.xar Expected outcome: ClamAV scanning process terminates with a crash
Protection:
- Immediate Upgrade: Update ClamAV to version 1.4.6, 1.5.4, or later immediately.
- For Cisco Secure Endpoint Users: Deploy Cisco-provided Secure Endpoint Connector updates as they become available in August 2026.
- Standalone ClamAV Users: Upgrade directly to ClamAV version 1.5.4 or later from the official repository.
- Temporary Mitigation: If patching is not immediately possible, limit or isolate ClamAV scanning of untrusted archive content, especially inputs that may contain XAR data.
- Monitor Logs: Review endpoint monitoring for unexpected ClamAV process terminations and confirm that malware scanning services remain operational.
- Least Privilege: Run the scanning service with least privilege and operational safeguards so a scanner crash has limited service impact.
Impact:
- Denial of Service (Primary): Successful exploitation causes the ClamAV scanning process to terminate, resulting in a DoS condition that interrupts malware scanning operations.
- Service Disruption: Affected systems become unavailable for critical security functions, potentially leaving networks more vulnerable to other attacks during the period when the scanning process is compromised.
- Memory Corruption: The flaw involves memory corruption arising from improper bounds and size handling, which may permit broader consequences beyond process termination.
- Remote Exploitation: Attackers can exploit this vulnerability remotely without authentication, making it accessible across multiple threat surfaces including email attachments, web downloads, and file sharing protocols.
- Widespread Exposure: The vulnerability affects ClamAV versions 0.98.1 through 1.5.3, impacting numerous organizations relying on ClamAV for endpoint protection.
- Critical Severity: Cisco assigned a high-severity rating to Windows deployments, with a CVSS score of 7.5, indicating a significant risk.
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Sources:
Reported By: nvd.nist.gov
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