CVE-2026-20218: Cisco Snort 3 VBA decompression buffer overflow denial of service

CVE-2026-20218 · Severity: medium · CVSS 5.8 · Published 2026-10-21

A flaw in Snort 3's Visual Basic macro decompression engine allows remote attackers to crash the detection engine by sending crafted VBA data, disrupting network security monitoring. The vulnerability affects Snort 3 integrated into Cisco Secure Firewall Threat Defense and IOS XE-based routers and edge platforms. A successful attack causes the Snort detection engine to restart unexpectedly, creating a window where network intrusions may go undetected.

Technologies: Cisco IOS XE Unified Threat Defense, Cisco Secure Firewall Threat Defense, Cisco Snort 3. Vendors: Cisco.

Quick answers

Is CVE-2026-20218 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-20218 being exploited in the wild.
How severe is CVE-2026-20218?
Medium severity, with a CVSS score of 5.8, published 21 October 2026.
Which products and versions are affected?
Cisco Secure Firewall Threat Defense 7.2.0 and later.
Is there a fix for CVE-2026-20218?
No fixed version is recorded yet. VBA macro decompression is not enabled by default; disable Snort 3 VBA macro decompression on intrusion policies if this feature is not required for your security posture. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-20218 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-20218?
Check whether you run Cisco IOS XE Unified Threat Defense, Cisco Secure Firewall Threat Defense or Cisco Snort 3 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

VBA macro decompression is not enabled by default; disable Snort 3 VBA macro decompression on intrusion policies if this feature is not required for your security posture.

Technical details

The vulnerability stems from improper range checking in the Snort 3 VBA decompression engine when processing user-controlled VBA macro data, leading to a stack-based buffer overflow. An unauthenticated remote attacker can exploit this by sending crafted VBA data (via IMAP, SMTP, HTTP, or POP3) to a device with Snort 3 active and VBA macro decompression enabled. A successful exploit causes the Snort 3 Detection Engine to restart, resulting in denial of service; VBA macro decompression is not enabled by default, limiting exposure.

Affected products

  • Cisco Snort 3
  • Cisco Secure Firewall Threat Defense 7.2.0 and later
  • Cisco IOS XE Unified Threat Defense

Timeline

  • 2026-10-21: disclosed

References

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