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CVE-2026-20243 Cisco CVE debrief

CVE-2026-20243 is a high-severity vulnerability in the ALZ file format parser of ClamAV, which could allow an unauthenticated, remote attacker to cause a DoS condition or potentially other expanded impacts due to memory corruption on an affected device. This vulnerability is caused by improper boundary checks for content in ALZ files during scanning, potentially leading to an out-of-bounds buffer write. An attacker could exploit this vulnerability by submitting a crafted file containing 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.

Vendor
Cisco
Product
Secure Endpoint
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-01
Original CVE updated
2026-07-09
Advisory published
2026-07-01
Advisory updated
2026-07-09

Who should care

Organizations using Cisco Secure Endpoint and ClamAV should prioritize patching this vulnerability to prevent potential DoS conditions and other impacts. Cisco Secure Endpoint versions prior to 1.27.2 for macOS, 1.29.0 for Linux, and 8.6.2 for Windows are affected, as well as ClamAV versions between 1.4.0 and 1.4.5, and 1.5.0 and 1.5.3.

Technical summary

The vulnerability exists in the ALZ file format parser of ClamAV, used in Cisco Secure Endpoint. It is caused by improper boundary checks during scanning, which may result in an out-of-bounds buffer write. An unauthenticated, remote attacker could exploit this by submitting a crafted ALZ file, potentially causing a DoS condition or other impacts due to memory corruption. Affected product deployments include Cisco Secure Endpoint versions prior to 1.27.2 for macOS, 1.29.0 for Linux, and 8.6.2 for Windows, as well as ClamAV versions between 1.4.0 and 1.4.5, and 1.5.0 and 1.5.3. Organizations should review Cisco's vendor advisory for specific guidance on affected versions and patches. Confirming the existence of affected deployments and planning for vendor-supported updates or mitigations is crucial.

Defensive priority

High

Recommended defensive actions

  • Apply patches or updates provided by Cisco for Secure Endpoint and ClamAV
  • Restrict access to ClamAV scanning services from untrusted sources
  • Implement network segmentation to limit the spread of potential attacks
  • Monitor ClamAV logs for suspicious activity or errors
  • Consider using compensating controls such as Web Application Firewalls

Evidence notes

The CVE record was published on 2026-07-01T17:16:30.423Z and was last modified on 2026-07-09T18:03:17.357Z. The NVD entry is currently Analyzed. Cisco has provided a vendor advisory for this vulnerability.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-01T17:16:30.423Z and has not been modified since then. The NVD entry is currently Analyzed.