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SnortApplication · Cisco

CVE-2026-20066

MEDIUM · 5.8 CVSS v3.1 Published 2026-03-04
Fix available
A fix is available. Upgrade to 3.9.7.0 or later.
See remediation →
67/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a denial-of-service vulnerability in Cisco's Snort 3 Detection Engine where the JSTokenizer normalization logic contains an error when processing JavaScript during HTTP inspection. An unauthenticated remote attacker can send crafted HTTP packets through an established connection to trigger an unexpected Snort 3 Detection Engine restart, interrupting packet inspection. Note that JSTokenizer must be explicitly enabled for exploitation.

MitigationApply Cisco patches when available, or if JSTokenizer is not required, disable it as a workaround. The vulnerability is only exploitable when JSTokenizer is enabled in the Snort 3 configuration.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
SnortApplication
Affected:>= 3.0.0-233, < 3.9.7.0
Secure Firewall Threat DefenseApplication
Affected:= 7.4.0= 7.4.1= 7.4.1.1= 7.4.2= 7.4.2.1= 7.4.2.2= 7.4.2.3= 7.4.2.4= 7.4.3= 7.6.0= 7.6.1= 7.6.2
Unified Threat Defense Snort Intrusion Prevention System EngineOperating system
Affected:= 17.2.1r= 17.3.1a= 17.3.2= 17.3.3= 17.3.4= 17.3.4a= 17.3.5= 17.3.6= 17.3.7= 17.3.8= 17.3.8a= 17.4.1a

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Snort 3 installation and version
    Run 'snort -V' or 'snort3 -V' to display the installed Snort 3 version. Compare this version against the Cisco advisory for CVE-2026-20066 to determine if it falls within the affected version range.
    Affected if The installed Snort 3 version is within the vulnerable range and no patch has been applied.
  2. Locate Snort 3 configuration file
    Common default locations are /etc/snort/snort.lua or /usr/local/etc/snort/snort.lua. The configuration file may also be specified via the -c flag when Snort starts.
    Affected if Unable to locate the active Snort 3 configuration file for inspection.
  3. Check if JSTokenizer is enabled
    Search the Snort 3 configuration file (e.g., snort.lua) for 'JSTokenizer' or 'js_normalizer' settings. Look for entries like 'js_normalizer = { enable = true }' or similar JSTokenizer-related configuration blocks.
    Affected if JSTokenizer normalization is explicitly enabled in the Snort 3 configuration (the vulnerability requires this setting to be active for exploitation).
  4. Verify HTTP inspection is active
    In the Snort 3 configuration, confirm that HTTP inspector or http_inspect is enabled. Check for 'http_inspect' or 'http_server' in the configuration and ensure it references or loads the JSTokenizer component.
    Affected if HTTP inspection is enabled and configured to use JSTokenizer for JavaScript normalization during traffic inspection.

A user is affected if they are running a vulnerable Snort 3 version with JSTokenizer explicitly enabled in the configuration for HTTP traffic inspection.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 3.9.7.0 or later
Fixed in 3.9.7.0
Interim mitigation

Apply Cisco patches when available, or if JSTokenizer is not required, disable it as a workaround. The vulnerability is only exploitable when JSTokenizer is enabled in the Snort 3 configuration.

Fix this in Snort Scoped from the published advisory
  • Consultation4.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,300
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-20066 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data