Cisco Snort sf_unfold_header Out-Of-Bounds Write Remote Code Execution Vulnerability

November 3rd, 2026
ZDI-26-867 ZDI-CAN-33575

CVE ID

CVE-2026-20043

CVSS Score

9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors

Cisco

Affected Products

Snort

Vulnerability Details

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Cisco Snort. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the processing of HTTP response bodies containing ZIP archives. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the Snort service account.

Additional Details

Cisco has issued an update to correct this vulnerability. More details can be found at:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-snort3-ybgmhTQe

Disclosure Timeline

  • 2026-10-28 - Vulnerability reported to vendor
  • 2026-11-03 - Coordinated public release of advisory
  • 2026-11-03 - Advisory Updated

Credit

Alex Williams from Pellera Technologies

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