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

CVE-2026-20243 is fixed in 39 products on 1 platform, first by clamav 1.5.3+dfsg-0ubuntu0.26.04.1, released July 1, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-20243
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0057
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 1, 2026
- Weakness: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20243

## Description

ALZ file format parser could allow an unauthenticated, remote attacker to cause a denial of service

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | clamav Debian 12.15 (bookworm) | 1.4.6+dfsg-0+deb12u1 | [DEBIAN-CVE-2026-20243](https://patchblox.com/security/data/fix/linux/debian-cve-2026-20243.md) | Jul 14, 2026 |
| Linux | clamav Debian 14 | 1.4.5+dfsg-1 | [DEBIAN-CVE-2026-20243](https://patchblox.com/security/data/fix/linux/debian-cve-2026-20243.md) | Jul 14, 2026 |
| Linux | clamav Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav opensuse-leap 16.0 | 1.5.3-160000.1.1 | [OPENSUSE-SU-2026:21252-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21252-1.md) | Jul 7, 2026 |
| Linux | clamav sles 15.6 | 1.5.3-150600.18.28.1 | [SUSE-SU-2026:2835-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2835-1.md) | Jul 9, 2026 |
| Linux | clamav sles 15.7 | 1.5.3-150600.18.28.1 | [SUSE-SU-2026:2835-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2835-1.md) | Jul 9, 2026 |
| Linux | clamav sles 16.0 | 1.5.3-160000.1.1 | [SUSE-SU-2026:22574-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22574-1.md) | Jul 7, 2026 |
| Linux | clamav-base Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-base 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-base-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav-base Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-base 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-base-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav-base Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-base 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-base-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav-daemon Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-daemon 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-daemon-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav-daemon Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-daemon 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-daemon-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav-daemon Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-daemon 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-daemon-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav-docs Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-docs 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-docs-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 21, 2026 |
| Linux | clamav-docs Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-docs 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-docs-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 21, 2026 |
| Linux | clamav-docs Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-docs 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-docs-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav-freshclam Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-freshclam 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-freshclam-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav-freshclam Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-freshclam 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-freshclam-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav-freshclam Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-freshclam 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-freshclam-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav-milter Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-milter 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-milter-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav-milter Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-milter 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-milter-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav-milter Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-milter 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-milter-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav-testfiles Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamav-testfiles 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamav-testfiles-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamav-testfiles Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamav-testfiles 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamav-testfiles-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamav-testfiles Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamav-testfiles 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamav-testfiles-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | clamav1.4 amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-data amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-debuginfo amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-debugsource amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-devel amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-doc amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-filesystem amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-freshclam amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-freshclam-debuginfo amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-lib amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-lib-debuginfo amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-milter amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.4-milter-debuginfo amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamav1.5 amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-data amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-debuginfo amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-debugsource amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-devel amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-doc amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-filesystem amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-freshclam amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-freshclam-debuginfo amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-lib amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-lib-debuginfo amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-milter amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamav1.5-milter-debuginfo amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamd1.4 amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamd1.4-debuginfo amzn 2023 | 1.4.5-1.amzn2023.0.1 | [ALAS2023-2026-1956](https://patchblox.com/security/data/fix/linux/alas2023-2026-1956.md) | Jul 20, 2026 |
| Linux | clamd1.5 amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamd1.5-debuginfo amzn 2023 | 1.5.3-1.amzn2023.0.1 | [ALAS2023-2026-1955](https://patchblox.com/security/data/fix/linux/alas2023-2026-1955.md) | Jul 20, 2026 |
| Linux | clamdscan Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [clamdscan 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-clamdscan-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | clamdscan Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [clamdscan 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-clamdscan-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | clamdscan Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [clamdscan 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-clamdscan-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |
| Linux | libclamav12 Ubuntu 22.04.1 LTS (jammy) | 1.5.3+dfsg-0ubuntu0.22.04.2 | [libclamav12 1.5.3+dfsg-0ubuntu0.22.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libclamav12-1.5.3-dfsg-0ubuntu0.22.04.2.md) | Jul 9, 2026 |
| Linux | libclamav12 Ubuntu 24.04.5 LTS (noble) | 1.5.3+dfsg-0ubuntu0.24.04.1 | [libclamav12 1.5.3+dfsg-0ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libclamav12-1.5.3-dfsg-0ubuntu0.24.04.1.md) | Jul 9, 2026 |
| Linux | libclamav12 Ubuntu 26.04.1 LTS (resolute) | 1.5.3+dfsg-0ubuntu0.26.04.1 | [libclamav12 1.5.3+dfsg-0ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libclamav12-1.5.3-dfsg-0ubuntu0.26.04.1.md) | Jul 1, 2026 |

---

Data as of 2026-11-11T07:45:43Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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