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

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.

Published: 2020-10-21 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-3555 is rated Moderate Risk (50.4/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.60%). 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-2020-3555

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 2025-03-30 0.80% 0.60% -0.21%
2 2025-03-29 0.60% 0.80% +0.21%
3 2025-03-19 — 0.60% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-3555

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.8 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
 2.2 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]
7.8 2.0 HIGH
AV:N/AC:L/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:L)
Exploitation conditions are straightforward and predictable.
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.
 10.0 6.9 [email protected]

Weakness enumeration for CVE-2020-3555

Affected software / configurations for CVE-2020-3555

Vendor Product Version Raw CPE
cisco adaptive_security_appliance < 9.6.4.43 cpe:2.3:a:cisco:adaptive_security_appliance:*:*:*:*:*:*:*:*
cisco firepower_threat_defense <= 6.2.2 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 6.3.0, < 6.3.0.6 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 6.4.0, < 6.4.0.10 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense >= 6.5.0, < 6.5.0.5 cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco firepower_threat_defense 6.6.0 cpe:2.3:a:cisco:firepower_threat_defense:6.6.0:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.7.0, < 9.8.4.24 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.10.0, < 9.10.1.43 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.12.0, < 9.12.4.2 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.13.0, < 9.13.1.13 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.14.0, < 9.14.1.19 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*

References for CVE-2020-3555

cvelogic Threat Intelligence