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

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-10-27 · updated 2026-08-11
Weakness: CWE-121

Description

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.

Affected products

Cisco Adaptive Security Appliance: before 9.8.4.40 — fixed in 9.8.4.40
Cisco ASA Software: from 9.9.0 before 9.12.4.29; from 9.13.0 before 9.14.3.9; from 9.15.0 before 9.15.1.17; from 9.16.0 before 9.16.2.3 — fixed in 9.12.4.29, 9.14.3.9, 9.15.1.17, 9.16.2.3
Cisco Asa 5505 Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5512-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5515-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5525-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5545-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5555-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5580 Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Asa 5585-X Firmware: 009.012(004.024), 009.015(001), 009.015(001.015), 009.015(001.016), 009.016(001)
Cisco Firepower Threat Defense Software: before 6.4.0.13; from 6.5.0 before 6.6.5; from 6.7.0 before 6.7.0.3; from 7.0.0 before 7.0.1 — fixed in 6.4.0.13, 6.6.5, 6.7.0.3, 7.0.1

How to fix

Upgrade to a fixed version: Cisco Adaptive Security Appliance 9.8.4.40; Cisco ASA Software 9.12.4.29, 9.14.3.9, 9.15.1.17, 9.16.2.3; Cisco Firepower Threat Defense Software 6.4.0.13, 6.6.5, 6.7.0.3, 7.0.1. Check the vendor advisory for mitigations.

References

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