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SnortApplication · Cisco

CVE-2026-20067

MEDIUM · 5.8 CVSS v3.1 Published 2026-03-04
Fix available
A fix is available. Upgrade to 3.9.5.0 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 incomplete error checking when parsing the Multicast DNS fields of the HTTP header. An attacker could exploit this vulnerability by sending crafted HTTP packets through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause a DoS condition when the Snort 3 Detection Engine unexpectedly restarts.

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

A vulnerability exists in the Snort 3 detection engine used by multiple Cisco products. The flaw stems from incomplete error checking during parsing of Multicast DNS (mDNS) fields embedded in HTTP headers. An unauthenticated remote attacker can send crafted HTTP packets through an established connection containing malformed mDNS data, triggering an unexpected restart of the Snort 3 detection engine, resulting in denial of packet inspection services.

MitigationApply Cisco-supplied patches or updates to the Snort 3 detection engine for affected products. As an interim network-level workaround, consider filtering or blocking HTTP traffic containing unexpected mDNS字段 until the patch can be deployed.

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, < 3.9.5.0
Cyber VisionApplication
Affected:= 3.0.0= 3.0.1= 3.0.2= 3.0.3= 3.0.4= 3.0.5= 3.0.6= 3.1.0= 3.1.1= 3.1.2= 3.2.0= 3.2.1
Secure Firewall Threat DefenseApplication
Affected:= 7.0.0= 7.0.0.1= 7.0.1= 7.0.1.1= 7.0.2= 7.0.2.1= 7.0.3= 7.0.4= 7.0.5= 7.0.6= 7.0.6.1= 7.0.6.2
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. Identify Snort 3 installation and version
    Run 'snort3 -V' or check the installed package version via system package manager (e.g., 'dpkg -l | grep snort', 'rpm -qa | grep snort', or 'snort --version'). Compare the version number against any available Snort 3 release notes for CVE-2026-20067 fixes.
    Affected if Snort 3 version is present but lacks the patch for this CVE (version prior to fix release)
  2. Verify HTTP preprocessor/inspector is enabled
    Examine Snort 3 configuration file (typically snort.lua or snort.conf) for 'http_inspect' or 'http' inspector being loaded and active. Search for lines containing 'http_inspect' or 'http' in the http section.
    Affected if HTTP inspection is enabled, as the vulnerability is triggered via malformed mDNS data in HTTP headers
  3. Confirm mDNS parsing within HTTP traffic inspection is active
    In the Snort 3 config, check if mDNS-related inspection is configured within the HTTP inspector or if there are any mDNS-related settings enabled. Look for 'mdns' keywords in the configuration file and examine http inspector parameters.
    Affected if mDNS fields are being parsed or inspected within HTTP traffic context, enabling the attack vector
  4. Check for traffic inspection on established connections
    Verify that Snort 3 is actively inspecting HTTP traffic flows. Review inline/IPS mode configuration and ensure stream tracking is enabled. This can be confirmed via 'snort -c <config> --lua-list' to list loaded modules or by reviewing the running configuration.
    Affected if Snort 3 is inline and actively inspecting HTTP traffic on established connections, allowing the crafted packets to reach the vulnerable code path

Environment is affected if running a Snort 3 version lacking the CVE-2026-20067 patch while HTTP inspection with mDNS parsing in HTTP headers is enabled and actively processing traffic.

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 3.9.5.0 or later
Fixed in 3.9.5.0
Interim mitigation

Apply Cisco-supplied patches or updates to the Snort 3 detection engine for affected products. As an interim network-level workaround, consider filtering or blocking HTTP traffic containing unexpected mDNS字段 until the patch can be deployed.

Fix this in Snort Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2026-20067 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