CVE-2021-40118 | Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Denial of Service Vulnerabilities

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a denial of service (DoS) condition. This vulnerability is due to improper input validation when parsing HTTPS requests. An attacker could exploit this vulnerability by sending a malicious HTTPS request to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

Published: 2021-10-27 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40118 is rated Moderate Risk (58.8/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.31%). EPSS rose +1.04% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-40118

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.26% 1.31% +1.04%
2 2025-11-21 0.36% 0.26% -0.10%
3 2025-11-18 — 0.36% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40118

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.6 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 4.0 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.1 2.0 HIGH
AV:N/AC:M/Au:N/C:N/I:N/A:C Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:C)
Complete availability impact.
 8.6 6.9 [email protected]

Weakness enumeration for CVE-2021-40118

Affected software / configurations for CVE-2021-40118

Vendor Product Version Raw CPE
cisco adaptive_security_appliance < 9.8.4.40 cpe:2.3:a:cisco:adaptive_security_appliance:*:*:*:*:*:*:*:*
cisco firepower_threat_defense < 6.4.0.13 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 6.5.0, < 6.6.5 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 6.7.0, < 6.7.0.3 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 7.0.0, < 7.0.1 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.9.0, < 9.12.4.29 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.13.0, < 9.14.3.9 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.15.0, < 9.15.1.17 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.16.0, < 9.16.2.3 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco asa_5512-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5512-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5512-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5512-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5512-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5512-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5512-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5512-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5512-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5512-x_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5505_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5505_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5505_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5505_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5505_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5505_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5505_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5505_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5505_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5505_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5515-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5515-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5515-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5515-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5515-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5515-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5515-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5515-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5515-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5515-x_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5525-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5525-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5525-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5525-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5525-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5525-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5525-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5525-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5525-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5525-x_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5545-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5545-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5545-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5545-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5545-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5545-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5545-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5545-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5545-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5545-x_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5555-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5555-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5555-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5555-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5555-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5555-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5555-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5555-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5555-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5555-x_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5580_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5580_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5580_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5580_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5580_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5580_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5580_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5580_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5580_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5580_firmware:009.016\(001\):*:*:*:*:*:*:*
cisco asa_5585-x_firmware 009.012\(004.024\) cpe:2.3:o:cisco:asa_5585-x_firmware:009.012\(004.024\):*:*:*:*:*:*:*
cisco asa_5585-x_firmware 009.015\(001\) cpe:2.3:o:cisco:asa_5585-x_firmware:009.015\(001\):*:*:*:*:*:*:*
cisco asa_5585-x_firmware 009.015\(001.015\) cpe:2.3:o:cisco:asa_5585-x_firmware:009.015\(001.015\):*:*:*:*:*:*:*
cisco asa_5585-x_firmware 009.015\(001.016\) cpe:2.3:o:cisco:asa_5585-x_firmware:009.015\(001.016\):*:*:*:*:*:*:*
cisco asa_5585-x_firmware 009.016\(001\) cpe:2.3:o:cisco:asa_5585-x_firmware:009.016\(001\):*:*:*:*:*:*:*

References for CVE-2021-40118

cvelogic Threat Intelligence