CVE-2026-20243 ClamAV ALZ Archive Processing Denial of Service Vulnerability

High 7.5 Published 1 Jul 2026 Updated 1 Jul 2026

An unauthenticated remote attacker can cause a denial of service in ClamAV by submitting a crafted ALZ file that triggers memory corruption.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-20243?

CVE-2026-20243 is a high-severity memory corruption vulnerability in Clamav Clamav, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A vulnerability in the ALZ file format parser of ClamAV could allow an unauthenticated, remote attacker to cause a DoS condition, or possibly other expanded impacts, resulting from memory corruption on an affected device. This vulnerability is due to improper boundary checks for content in ALZ files during scanning, which may result in an out-of-bounds buffer write. An attacker could exploit this vulnerability by submitting a crafted file that contains ALZ content to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to cause the ClamAV scanning process to terminate, resulting in a DoS condition on the affected software.

Weakness: CWE-120

Which versions are affected by CVE-2026-20243?

It affects 2 products.

Products include Cisco Secure Endpoint, Clamav Clamav.

How do I fix CVE-2026-20243?

Upgrade to a fixed version.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-20243 being exploited?

There is no known exploitation of CVE-2026-20243 in the wild and no public exploit code.

All Clamav Clamav vulnerabilities

Sources

Also known as AZL-92178, DEBIAN-CVE-2026-20243, GHSA-v85g-hcf7-wr7c, MINI-gp9w-hv5w-8q4c, MINI-vh2q-hj27-g2wr, UBUNTU-CVE-2026-20243.