#VU67766 Improper access control in Cisco Systems, Inc products - CVE-2021-27854

Vulnerability identifier: #VU67766

Vulnerability risk: Low

CVSSv4.0: 1.3 [CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2021-27854

CWE-ID: CWE-284

Exploitation vector: Local network

Exploit availability: No

Vulnerable software:
6300 Series Embedded Services Access Points
Other software / Other software solutions
Aironet 4800 Access Points
Other software / Other software solutions
Business 100 Series Access Points
Other software / Other software solutions
Business 200 Series Access Points
Other software / Other software solutions
Wireless LAN Controller Software
Other software / Other software solutions
Cisco Aironet 1540 Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Aironet 1560 Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Aironet 1800 Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Aironet 2800 Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Aironet 3800 Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Catalyst 9100 Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Catalyst IW 6300 Heavy Duty Series Access Points
Hardware solutions / Routers & switches, VoIP, GSM, etc
Integrated AP on 1100 Integrated Services Routers
Hardware solutions / Routers & switches, VoIP, GSM, etc
Catalyst 9800 Wireless Controller Software
Hardware solutions / Routers & switches, VoIP, GSM, etc

Vendor: Cisco Systems, Inc

Description

The vulnerability allows a remote attacker to gain unauthorized access to otherwise restricted functionality.

The vulnerability exists due to improper access restrictions in the Layer 2 network filtering capabilities such as IPv6 RA guard. A remote attacker on the local network can bypass these capabilities using a combination of VLAN 0 headers, LLC/SNAP headers in Ethernet to Wifi frame translation and in the reverse-Wifi to Ethernet.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

6300 Series Embedded Services Access Points: All versions

Cisco Aironet 1540 Series Access Points: All versions

Aironet 1560 Series Access Points: All versions

Aironet 1800 Series Access Points: All versions

Aironet 2800 Series Access Points: All versions

Aironet 3800 Series Access Points: All versions

Aironet 4800 Access Points: All versions

Business 100 Series Access Points: All versions

Business 200 Series Access Points: All versions

Catalyst 9100 Access Points: All versions

Catalyst IW 6300 Heavy Duty Series Access Points: All versions

Integrated AP on 1100 Integrated Services Routers: All versions

Wireless LAN Controller Software: 8.5 - 8.10

Catalyst 9800 Wireless Controller Software: 17.2 - 17.6.2

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External links
https://blog.champtar.fr/VLAN0_LLC_SNAP/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.