CVE-2021-34787 [Medium] | Security Bypass in Adaptive Security Appliance

A vulnerability in the identity-based firewall (IDFW) rule processing feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass security protections. This vulnerability is due to improper handling of network requests by affected devices configured to use object group search. An attacker could exploit this vulnerability by sending a specially crafted network request to an affected device. A successful exploit could allow the attacker to bypass access control list (ACL) rules on the device, bypass security protections, and send network traffic to unauthorized hosts.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-11-21	0.40%	1.15%	+0.75%
2	2025-11-18	1.15%	0.40%	-0.75%
3	2025-09-12	—	1.15%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-11-21

0.40%

1.15%

+0.75%

2025-11-18

1.15%

0.40%

-0.75%

2025-09-12

—

1.15%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.3	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N` 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:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	3.9	1.4	[email protected]
5.3	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N` 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:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	3.9	1.4	[email protected]
4.3	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:N/I:P/A:N` 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:P) Partial integrity impact. Availability impact (A:N) No availability impact.	8.6	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.3

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N 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:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

3.9

1.4

[email protected]

5.3

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N 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:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

3.9

1.4

[email protected]

4.3

2.0

MEDIUM

AV:N/AC:M/Au:N/C:N/I:P/A:N 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:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

8.6

2.9

[email protected]

Affected software / configurations for CVE-2021-34787

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, < 9.12.4.25	cpe:2.3:o:cisco:adaptive_security_appliance_software::::::::
cisco	adaptive_security_appliance_software	>= 9.13.0, < 9.14.3.1	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, < 9.16.1.28	cpe:2.3:o:cisco:adaptive_security_appliance_software::::::::
cisco	asa_5512-x_firmware	009.009	cpe:2.3:o:cisco:asa_5512-x_firmware:009.009:::::::*
cisco	asa_5512-x_firmware	009.012	cpe:2.3:o:cisco:asa_5512-x_firmware:009.012:::::::*
cisco	asa_5505_firmware	009.009	cpe:2.3:o:cisco:asa_5505_firmware:009.009:::::::*
cisco	asa_5505_firmware	009.012	cpe:2.3:o:cisco:asa_5505_firmware:009.012:::::::*
cisco	asa_5515-x_firmware	009.009	cpe:2.3:o:cisco:asa_5515-x_firmware:009.009:::::::*
cisco	asa_5515-x_firmware	009.012	cpe:2.3:o:cisco:asa_5515-x_firmware:009.012:::::::*
cisco	asa_5525-x_firmware	009.009	cpe:2.3:o:cisco:asa_5525-x_firmware:009.009:::::::*
cisco	asa_5525-x_firmware	009.012	cpe:2.3:o:cisco:asa_5525-x_firmware:009.012:::::::*
cisco	asa_5545-x_firmware	009.009	cpe:2.3:o:cisco:asa_5545-x_firmware:009.009:::::::*
cisco	asa_5545-x_firmware	009.012	cpe:2.3:o:cisco:asa_5545-x_firmware:009.012:::::::*
cisco	asa_5555-x_firmware	009.009	cpe:2.3:o:cisco:asa_5555-x_firmware:009.009:::::::*
cisco	asa_5555-x_firmware	009.012	cpe:2.3:o:cisco:asa_5555-x_firmware:009.012:::::::*
cisco	asa_5580_firmware	009.009	cpe:2.3:o:cisco:asa_5580_firmware:009.009:::::::*
cisco	asa_5580_firmware	009.012	cpe:2.3:o:cisco:asa_5580_firmware:009.012:::::::*
cisco	asa_5585-x_firmware	009.009	cpe:2.3:o:cisco:asa_5585-x_firmware:009.009:::::::*
cisco	asa_5585-x_firmware	009.012	cpe:2.3:o:cisco:asa_5585-x_firmware:009.012:::::::*

References for CVE-2021-34787

URL	Tags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-rule-bypass-ejjOgQEY	Vendor Advisory

URL

CVE-2021-34787 | Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Identity-Based Rule Bypass Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2021-34787

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34787

Weakness enumeration for CVE-2021-34787

Affected software / configurations for CVE-2021-34787

References for CVE-2021-34787