Secure Firewall Management CenterApplication · Cisco
CVE-2021-40116
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 · uneditedMultiple Cisco products are affected by a vulnerability in Snort rules that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.The vulnerability is due to improper handling of the Block with Reset or Interactive Block with Reset actions if a rule is configured without proper constraints. An attacker could exploit this vulnerability by sending a crafted IP packet to the affected device. A successful exploit could allow the attacker to cause through traffic to be dropped. Note: Only products with Snort3 configured and either a rule with Block with Reset or Interactive Block with Reset actions configured are vulnerable. Products configured with Snort2 are not vulnerable.
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 confidenceThis CVE affects Cisco products running Snort3 (not Snort2) with configured rules using 'Block with Reset' or 'Interactive Block with Reset' actions. The vulnerability stems from improper handling of these actions when rules lack proper constraints. An unauthenticated remote attacker can exploit this by sending crafted IP packets, causing legitimate through traffic to be dropped and resulting in a denial of service condition.
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
Secure Firewall Management CenterApplication
= 3.1.0.1
Secure Firewall Threat DefenseApplication
>= 6.4.0, < 6.4.0.13>= 6.6.0, < 6.6.5.1>= 6.7.0, < 6.7.0.3>= 7.0.0, < 7.0.1
SnortApplication
>= 3.0.0.0, < 3.1.0.100CVSS 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
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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 checksWork through these to decide whether this CVE applies to you.
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Identify the Snort version in useCheck the running Snort binary or package version using 'snort -V' or inspect the installed package version via the system package managerAffected if The system is running Snort3 (snort3) rather than Snort2 - this vulnerability only affects Snort3
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Verify the Snort3 version against affected rangesCompare the installed Snort3 version to the affected ranges: Cisco Firepower Threat Defense versions listed, Cisco Secure Firewall Management Center version 3.1.0.1, or Cisco Snort versions >= 3.0.0.0 and < 3.1.0.100Affected if The installed version falls within any of the listed affected version ranges
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Check for Snort3 rules with Block actionsInspect the Snort3 rule configuration files or policy rules for any rules using 'Block with Reset' or 'Interactive Block with Reset' action keywordsAffected if Any rules with 'block with reset' or 'interactive block with reset' actions are configured in the Snort3 policy
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Review if Block rules have proper constraintsExamine each Block with Reset or Interactive Block with Reset rule to determine if it has proper constraints defined such as source/destination IP, port, or other matching criteria that limit the rule scopeAffected if One or more Block with Reset or Interactive Block with Reset rules lack proper constraints and could match arbitrary traffic
A system is affected if it runs Snort3 within the specified version ranges AND has configured Block with Reset or Interactive Block with Reset rules without proper constraints, allowing an attacker to cause legitimate traffic drops.
Generated from the published advisory. Verify against your own configuration.
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.
dbcve · scoped3.1.0.1006.4.0.136.6.5.1
Organizations should audit Snort3 rules for any Block with Reset or Interactive Block with Reset actions and ensure they have proper constraints defined. Consider migrating to Snort2 if Snort3 is not required, as Snort2 is not vulnerable to this issue.
Snort 3.1.0.100+; Firepower Threat Defense 6.4.0.13+, 6.6.5.1+, 7.0.0.3+, or 7.0.1+ depending on current branch
- 1. Identify the currently installed Snort version on the affected device using 'snort -V' or through the management interface.
- 2. If running Snort3 (not Snort2), identify any rules configured with 'Block with Reset' or 'Interactive Block with Reset' actions.
- 3. For Firepower Threat Defense: Upgrade to the minimum fixed version for your current branch: 6.4.0.13 (for 6.4.x), 6.6.5.1 (for 6.6.x), 7.0.0.3 (for 6.7.x), or 7.0.1 (for 7.0.x).
- 4. For Snort: Upgrade to version 3.1.0.100 or later.
- 5. After upgrade, verify the Snort3 version is no longer vulnerable using 'snort -V'.
- 6. Test that security policies with Block with Reset actions function correctly post-upgrade.
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Secure Firewall Management Center
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-40116 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-40116 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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