CVE-2021-34770 [Critical] | Denial of Service in Ios Xe

A vulnerability in the Control and Provisioning of Wireless Access Points (CAPWAP) protocol processing of Cisco IOS XE Software for Cisco Catalyst 9000 Family Wireless Controllers could allow an unauthenticated, remote attacker to execute arbitrary code with administrative privileges or cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a logic error that occurs during the validation of CAPWAP packets. An attacker could exploit this vulnerability by sending a crafted CAPWAP packet to an affected device. A successful exploit could allow the attacker to execute arbitrary code with administrative privileges or cause the affected device to crash and reload, resulting in a DoS condition.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-12-28	1.15%	1.03%	-0.12%
2	2025-12-27	1.03%	1.15%	+0.12%
3	2025-11-21	—	1.03%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-12-28

1.15%

1.03%

-0.12%

2025-12-27

1.03%

1.15%

+0.12%

2025-11-21

—

1.03%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
10.0	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	6.0	[email protected]
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
9.0	2.0	HIGH	`AV:N/AC:L/Au:S/C:C/I:C/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:S) A single authentication is required. Confidentiality impact (C:C) Complete confidentiality impact. Integrity impact (I:C) Complete integrity impact. Availability impact (A:C) Complete availability impact.	8.0	10.0	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

10.0

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

6.0

[email protected]

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

5.9

[email protected]

9.0

2.0

HIGH

AV:N/AC:L/Au:S/C:C/I:C/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:S): A single authentication is required.
Confidentiality impact (C:C): Complete confidentiality impact.
Integrity impact (I:C): Complete integrity impact.
Availability impact (A:C): Complete availability impact.

8.0

10.0

[email protected]

Affected software / configurations for CVE-2021-34770

Vendor	Product	Version	Raw CPE
cisco	ios_xe	—	cpe:2.3:o:cisco:ios_xe:-:::::::*
cisco	ios_xe	3.15.1xbs	cpe:2.3:o:cisco:ios_xe:3.15.1xbs:::::::*
cisco	ios_xe	3.15.2xbs	cpe:2.3:o:cisco:ios_xe:3.15.2xbs:::::::*
cisco	ios_xe	16.6.4s	cpe:2.3:o:cisco:ios_xe:16.6.4s:::::::*
cisco	ios_xe	16.10.1	cpe:2.3:o:cisco:ios_xe:16.10.1:::::::*
cisco	ios_xe	16.10.1e	cpe:2.3:o:cisco:ios_xe:16.10.1e:::::::*
cisco	ios_xe	16.10.1s	cpe:2.3:o:cisco:ios_xe:16.10.1s:::::::*
cisco	ios_xe	16.11.1	cpe:2.3:o:cisco:ios_xe:16.11.1:::::::*
cisco	ios_xe	16.11.1a	cpe:2.3:o:cisco:ios_xe:16.11.1a:::::::*
cisco	ios_xe	16.11.1b	cpe:2.3:o:cisco:ios_xe:16.11.1b:::::::*
cisco	ios_xe	16.11.1c	cpe:2.3:o:cisco:ios_xe:16.11.1c:::::::*
cisco	ios_xe	16.11.2	cpe:2.3:o:cisco:ios_xe:16.11.2:::::::*
cisco	ios_xe	16.12.1	cpe:2.3:o:cisco:ios_xe:16.12.1:::::::*
cisco	ios_xe	16.12.1s	cpe:2.3:o:cisco:ios_xe:16.12.1s:::::::*
cisco	ios_xe	16.12.1t	cpe:2.3:o:cisco:ios_xe:16.12.1t:::::::*
cisco	ios_xe	16.12.2s	cpe:2.3:o:cisco:ios_xe:16.12.2s:::::::*
cisco	ios_xe	16.12.2t	cpe:2.3:o:cisco:ios_xe:16.12.2t:::::::*
cisco	ios_xe	16.12.3	cpe:2.3:o:cisco:ios_xe:16.12.3:::::::*
cisco	ios_xe	16.12.3s	cpe:2.3:o:cisco:ios_xe:16.12.3s:::::::*
cisco	ios_xe	16.12.4	cpe:2.3:o:cisco:ios_xe:16.12.4:::::::*
cisco	ios_xe	16.12.4a	cpe:2.3:o:cisco:ios_xe:16.12.4a:::::::*
cisco	ios_xe	17.1.1	cpe:2.3:o:cisco:ios_xe:17.1.1:::::::*
cisco	ios_xe	17.1.1s	cpe:2.3:o:cisco:ios_xe:17.1.1s:::::::*
cisco	ios_xe	17.1.1t	cpe:2.3:o:cisco:ios_xe:17.1.1t:::::::*
cisco	ios_xe	17.1.2	cpe:2.3:o:cisco:ios_xe:17.1.2:::::::*
cisco	ios_xe	17.1.3	cpe:2.3:o:cisco:ios_xe:17.1.3:::::::*
cisco	ios_xe	17.2.1	cpe:2.3:o:cisco:ios_xe:17.2.1:::::::*
cisco	ios_xe	17.2.1a	cpe:2.3:o:cisco:ios_xe:17.2.1a:::::::*
cisco	ios_xe	17.3.1	cpe:2.3:o:cisco:ios_xe:17.3.1:::::::*

References for CVE-2021-34770

URL	Tags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-rce-LYgj8Kf	Vendor Advisory

URL

CVE-2021-34770 | Cisco IOS XE Software for Catalyst 9000 Family Wireless Controllers CAPWAP Remote Code Execution Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2021-34770

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34770

Weakness enumeration for CVE-2021-34770

Affected software / configurations for CVE-2021-34770

References for CVE-2021-34770