CVE-2020-3436 [High] | File Upload / RCE in Adaptive Security Appliance

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to upload arbitrary-sized files to specific folders on an affected device, which could lead to an unexpected device reload. The vulnerability exists because the affected software does not efficiently handle the writing of large files to specific folders on the local file system. An attacker could exploit this vulnerability by uploading files to those specific folders. A successful exploit could allow the attacker to write a file that triggers a watchdog timeout, which would cause the device to unexpectedly reload, causing a denial of service (DoS) condition.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-11-21	1.30%	2.15%	+0.85%
2	2025-11-18	2.15%	1.30%	-0.85%
3	2025-03-30	—	2.15%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-11-21

1.30%

2.15%

+0.85%

2025-11-18

2.15%

1.30%

-0.85%

2025-03-30

—

2.15%

—

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]
8.6	3.0	HIGH	`CVSS:3.0/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]
7.8	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]

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]

8.6

3.0

HIGH

CVSS:3.0/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]

7.8

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]

Affected software / configurations for CVE-2020-3436

Vendor	Product	Version	Raw CPE
cisco	adaptive_security_appliance	< 9.6.4.45	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	>= 9.8.0, < 9.8.4.25	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, < 9.10.1.44	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, < 9.13.1.12	cpe:2.3:o:cisco:adaptive_security_appliance_software::::::::
cisco	adaptive_security_appliance_software	>= 9.14.0, < 9.14.1.15	cpe:2.3:o:cisco:adaptive_security_appliance_software::::::::

References for CVE-2020-3436

URL	Tags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-fileup-dos-zvC7wtys	Vendor Advisory

URL

CVE-2020-3436 | Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services File Upload Denial of Service Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2020-3436

Common vulnerability scoring system (CVSS) metrics for CVE-2020-3436

Weakness enumeration for CVE-2020-3436

Affected software / configurations for CVE-2020-3436

References for CVE-2020-3436