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ClamAV CVE-2026-20243

| EUVDEUVD-2026-41086 HIGH
Classic Buffer Overflow (CWE-120)
2026-07-01 psirt@cisco.com GHSA-v85g-hcf7-wr7c
Buffer Overflow Secure Endpoint Clamav Red Hat Suse
7.5
CVSS 3.1 · Vendor: cisco
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Severity by source

Vendor (cisco) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
7.5 HIGH

ClamAV commonly scans remotely-delivered files with no auth or interaction (AV:N/AC:L/PR:N/UI:N); confirmed impact is a process crash only, so C:N/I:N/A:H.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
HIGH
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (cisco).

CVSS VectorVendor: cisco

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

1
Analysis Generated
Jul 01, 2026 - 17:40 vuln.today

DescriptionCVE.org

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.

AnalysisAI

Denial of service in ClamAV's ALZ archive parser allows an unauthenticated, remote attacker to crash the scanning engine by submitting a crafted ALZ file, with the vendor noting possible expanded impact beyond DoS. The flaw is a heap out-of-bounds write triggered during scanning, and because ClamAV is commonly deployed as an automated mail/upload gateway scanner, an attacker only needs to get a malicious file scanned. No public exploit identified at time of analysis, and the vulnerability is not listed in CISA KEV.

Technical ContextAI

ClamAV is a widely used open-source antivirus engine (maintained by Cisco Talos) that unpacks and inspects many archive and file formats, including the Korean ALZ compression format, to scan embedded content. The root cause is CWE-120 (buffer copy without checking size of input / classic buffer overflow): the ALZ parser performs improper boundary checks on content fields inside the archive, allowing attacker-controlled data to be written past the bounds of an allocated buffer (an out-of-bounds write). Format parsers like this run automatically inside the scanning daemon (clamd) or command-line scans, so a memory-corruption bug in the decompression path is directly reachable by any file the engine is asked to scan.

RemediationAI

Patch available per vendor advisory: upgrade ClamAV to the fixed release identified in the Cisco/Talos advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-clamav-88cFYyxR (the exact fixed version is not specified in the provided data - confirm the precise release from that advisory before deploying). As a compensating control until patched, disable ALZ archive scanning if your integration supports selectively excluding that format, or block/strip ALZ files at the mail or upload gateway before they reach the scanner; the trade-off is reduced coverage of legitimate ALZ archives and the effort of maintaining a file-type filter. Running clamd under a restricted, sandboxed service account with automatic restart limits the blast radius of a crash but does not remove the underlying flaw.

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Same weakness CWE-120 – Classic Buffer Overflow

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CVE-2017-7269 CRITICAL POC
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CVE-2019-11043 CRITICAL POC
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CVE-2016-10174 CRITICAL POC
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CVE-2016-0099 HIGH POC
7.8
CVE-2016-6366 HIGH POC
8.8
CVE-2013-1331 HIGH
7.8
CVE-2013-0641 HIGH
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CVE-2017-15222 CRITICAL POC
9.8

Same technique Buffer Overflow

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CVE-2017-7269 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
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CVE-2011-2462 CRITICAL POC
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CVE-2020-0796 CRITICAL POC
10.0
CVE-2019-11043 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: Important
Product Status
openSUSE Leap 16.0 Fixed
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected

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CVE-2026-20243 vulnerability details – vuln.today
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