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CVE-2021-40116

Multiple Cisco Products Snort Rule Denial of Service Vulnerability

HIGH
7.5
CVSS Score
Published: October 27, 2021 at 06:56 PM UTC
Updated: August 11, 2026 at 07:33 PM UTC
3 products affected across 1 vendorSecure Firewall Threat DefenseSecure Firewall Management CenterSnort++

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Severity
HIGH7.5
Exploit prediction
EPSS 1%
SSVC
No known exploit

Description

Multiple 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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Secure Firewall Management Center· Cisco
95%
3.1.0.1
Secure Firewall Threat Defense· Cisco
95%
6.4.0 ≤ v < 6.4.0.136.6.0 ≤ v < 6.6.5.16.7.0 ≤ v < 6.7.0.37.0.0 ≤ v < 7.0.1
Snort++· Cisco
95%
3.0.0.0 ≤ v < 3.1.0.100
Affected range stops below 3.1.0.100, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (1)

Vendor Advisoryx_refsource_CISCO
Source: [email protected]
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-dos-RywH7ezM

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGH[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-241NVD-CWE-noinfo

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