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CVE-2021-40116

25
FAUCET Score

CVE-2021-40116 is a denial-of-service (DoS) vulnerability in Cisco products utilizing Snort3 with specific "Block with Reset" or "Interactive Block with Reset" rules. An unauthenticated, remote attacker can exploit this by sending a crafted IP packet, causing affected devices like Cisco Firepower Threat Defense and Secure Firewall Management Center to drop legitimate network traffic. With a CVSS score of 7.5 (High), this vulnerability is easily exploitable over the network with low attack complexity, leading to a complete loss of availability. While there is no known active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), it has garnered significant community discussion and media coverage, indicating awareness within the cybersecurity landscape.

Impacted Technologies

VendorProductVersion(s)CPE
>= 6.4.0, < 6.4.0.13CPE matchmatch criteria
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
>= 6.6.0, < 6.6.5.1CPE matchmatch criteria
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
>= 6.7.0, < 6.7.0.3CPE matchmatch criteria
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
>= 7.0.0, < 7.0.1CPE matchmatch criteria
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
3.1.0.1CPE matchmatch criteria
cpe:2.3:a:cisco:secure_firewall_management_center:3.1.0.1:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.6HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
4.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.35%
Probability of exploitation in next 30 days
EPSS Percentile
68.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0135 is in the 49th percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Patches (1)

ciscovendor investigatingvia nvd_reference
View patch

References

tools.cisco.com / security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-dos-RywH7ezM
Vendor Advisory