CVE-2026-20066 Multiple Cisco Products Snort 3 TBD Denial of Service Vulnerability
An unauthenticated remote attacker can cause a denial of service in Cisco Snort 3 by sending crafted HTTP packets, requiring JSTokenizer to be enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20066?
CVE-2026-20066 is a medium-severity denial of service vulnerability in Cisco Secure Firewall Threat Defense, published on 4 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Multiple Cisco products are affected by a vulnerability in the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart, resulting in an interruption of packet inspection. This vulnerability is due to an error in the JSTokenizer normalization logic when the HTTP inspection normalizes JavaScript. An attacker could exploit this vulnerability by sending crafted HTTP packets through an established connection that is parsed by Snort 3. A successful exploit could allow the attacker to cause a DoS condition when the Snort 3 Detection Engine restarts unexpectedly. JSTokenizer is not enabled by default.
Weakness: CWE-400
Which versions are affected by CVE-2026-20066?
It affects 3 products.
Products include Cisco Secure Firewall Threat Defense, Cisco Snort, Cisco Unified Threat Defense Snort Intrusion Prevention System Engine.
How do I fix CVE-2026-20066?
No fix has been published for CVE-2026-20066 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-20066 being exploited?
There is no known exploitation of CVE-2026-20066 in the wild and no public exploit code.
Other vulnerabilities in Cisco Secure Firewall Threat Defense
- CVE-2024-20412 Hardcoded credentials in Cisco Firepower Threat Defense Software
- CVE-2024-20330 Memory corruption in Cisco Firepower Threat Defense Software
- CVE-2024-20339 Cisco Firepower Threat Defense Software for Firepower 2100 Series TLS Denial of Service Vulnerability
- CVE-2024-20351 Cisco Firepower Threat Defense Software Snort Firewall Denial of Service Vulnerability
- CVE-2023-20083 Denial of service in Cisco Firepower Threat Defense Software
Sources
Also known as GHSA-rcxv-vmj3-3mj9.