CVE-2026-20066
Received Received - Intake
Denial of Service in Cisco Snort 3 via JSTokenizer Flaw

Publication date: 2026-03-04

Last updated on: 2026-03-04

Assigner: Cisco Systems, Inc.

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.
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Meta Information
Published
2026-03-04
Last Modified
2026-03-04
Generated
2026-06-16
AI Q&A
2026-03-04
EPSS Evaluated
2026-06-14
NVD
CVE-2026-20066
EUVD
EUVD-2026-9465
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
cisco snort_3 *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.
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Executive Summary

This vulnerability affects multiple Cisco products that use the Snort 3 Detection Engine. It is caused by an error in the JSTokenizer normalization logic, which is part of the HTTP inspection process that normalizes JavaScript. An unauthenticated, remote attacker can exploit this by sending specially crafted HTTP packets through an established connection that Snort 3 parses.

Exploiting this vulnerability can cause the Snort 3 Detection Engine to restart unexpectedly, leading to an interruption in packet inspection.

It is important to note that JSTokenizer is not enabled by default.

Impact Analysis

The primary impact of this vulnerability is a Denial of Service (DoS) condition. An attacker can cause the Snort 3 Detection Engine to restart unexpectedly, which interrupts packet inspection.

This interruption could reduce the effectiveness of network security monitoring and intrusion detection, potentially allowing malicious traffic to go undetected during the downtime.

Compliance Impact

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Detection Guidance

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Mitigation Strategies

This vulnerability is due to an error in the JSTokenizer normalization logic, which is not enabled by default.

To mitigate this vulnerability, ensure that JSTokenizer is not enabled if it is not required.

Additionally, monitor for updates or patches from Cisco addressing this issue and apply them promptly to prevent potential denial of service conditions caused by the Snort 3 Detection Engine restarting unexpectedly.

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