CVE-2020-3555: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SIP Denial of Service Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-10-21 · updated 2026-08-11
Weakness: CWE-404

Description

A vulnerability in the SIP inspection process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to a watchdog timeout and crash during the cleanup of threads that are associated with a SIP connection that is being deleted from the connection list. An attacker could exploit this vulnerability by sending a high rate of crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a watchdog timeout and crash, resulting in a crash and reload of the affected device.

Affected products

Cisco Adaptive Security Appliance: before 9.6.4.43 — fixed in 9.6.4.43
Cisco ASA Software: from 9.7.0 before 9.8.4.24; from 9.9.0 before 9.9.2.80; from 9.10.0 before 9.10.1.43; from 9.12.0 before 9.12.4.2; from 9.13.0 before 9.13.1.13; from 9.14.0 before 9.14.1.19 — fixed in 9.10.1.43, 9.12.4.2, 9.13.1.13, 9.14.1.19, 9.8.4.24, 9.9.2.80
Cisco Firepower Threat Defense Software: through 6.2.2; from 6.3.0 before 6.3.0.6; from 6.4.0 before 6.4.0.10; from 6.5.0 before 6.5.0.5; 6.6.0 — fixed in 6.3.0.6, 6.4.0.10, 6.5.0.5

How to fix

Upgrade to a fixed version: Cisco Adaptive Security Appliance 9.6.4.43; Cisco ASA Software 9.10.1.43, 9.12.4.2, 9.13.1.13, 9.14.1.19; Cisco Firepower Threat Defense Software 6.3.0.6, 6.4.0.10, 6.5.0.5. Check the vendor advisory for mitigations.

References

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