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AUSCERT External Security Bulletin Redistribution
Cisco Aironet Access Points WLAN Control Protocol Packet
Buffer Leak Denial of Service Vulnerability
23 September 2021
AusCERT Security Bulletin Summary
Product: Aironet Access Points
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-34740
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Cisco Aironet Access Points WLAN Control Protocol Packet Buffer Leak Denial of
Advisory ID: cisco-sa-airo-wpa-pktleak-dos-uSTyGrL
First Published: 2021 September 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvu98674
CVE Names: CVE-2021-34740
o A vulnerability in the WLAN Control Protocol (WCP) implementation for Cisco
Aironet Access Point (AP) software could allow an unauthenticated, adjacent
attacker to cause a reload of an affected device, resulting in a denial of
service (DoS) condition.
This vulnerability is due to incorrect error handling when an affected
device receives an unexpected 802.11 frame. An attacker could exploit this
vulnerability by sending certain 802.11 frames over the wireless network to
an interface on an affected AP. A successful exploit could allow the
attacker to cause a packet buffer leak. This could eventually result in
buffer allocation failures, which would trigger a reload of the affected
Cisco has released software updates that address this vulnerability. There
are no workarounds that address this vulnerability.
This advisory is available at the following link:
o Vulnerable Products
This vulnerability affects the following Cisco products if they are running
a vulnerable release of Cisco Aironet AP software:
6300 Series Embedded Services APs
Aironet 1540 Series
Aironet 1560 Series
Aironet 1800 APs
Aironet 2800 Series APs
Aironet 3800 Series APs
Aironet 4800 APs
Catalyst 9100 APs
Catalyst IW6300 Heavy Duty Series APs
Integrated APs on 1100 Integrated Services Routers (ISRs)
Only the 8.10, 17.2, and 17.3 code trains are vulnerable. For information
about which Cisco software releases are vulnerable, see the Fixed Software
section of this advisory.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect any Cisco
Access Point series that is not listed in the Vulnerable Products section
of this advisory.
Indicators of Compromise
o Exploitation of this vulnerability causes the WCP daemon process to
unexpectedly restart and the AP to reload. This event would be indicated by
the following syslog messages:
systemd: wcpd.service: main process exited, code=dumped, status=6/ABRT
systemd: Unit wcpd.service entered failed state.
systemd: wcpd.service failed.
To view these syslog messages, use the show logging CLI command. If the AP
reloaded unexpectedly and these syslog messages are present, contact Cisco
Technical Assistance Center (TAC) to determine if this vulnerability was
exploited on the device.
o There are no workarounds that address this vulnerability.
o Cisco has released free software updates that address the vulnerability
described in this advisory. Customers may only install and expect support
for software versions and feature sets for which they have purchased a
license. By installing, downloading, accessing, or otherwise using such
software upgrades, customers agree to follow the terms of the Cisco
Additionally, customers may only download software for which they have a
valid license, procured from Cisco directly, or through a Cisco authorized
reseller or partner. In most cases this will be a maintenance upgrade to
software that was previously purchased. Free security software updates do
not entitle customers to a new software license, additional software
feature sets, or major revision upgrades.
When considering software upgrades , customers are advised to regularly
consult the advisories for Cisco products, which are available from the
Cisco Security Advisories page , to determine exposure and a complete
In all cases, customers should ensure that the devices to be upgraded
contain sufficient memory and confirm that current hardware and software
configurations will continue to be supported properly by the new release.
If the information is not clear, customers are advised to contact the Cisco
Technical Assistance Center (TAC) or their contracted maintenance
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service
contract and customers who make purchases through third-party vendors but
are unsuccessful in obtaining fixed software through their point of sale
should obtain upgrades by contacting the Cisco TAC: https://www.cisco.com/c
Customers should have the product serial number available and be prepared
to provide the URL of this advisory as evidence of entitlement to a free
The process to upgrade an AP requires administrators to upgrade the
wireless controller to which the AP is registered. Customers are advised to
upgrade to an appropriate fixed software release as indicated in the
Access Points Managed by Wireless LAN Controller or Mobility Express
Cisco Wireless LAN Controller Software Release First Fixed Release
8.9 and earlier Not vulnerable.
8.10 184.108.40.206 ^1
1. The first vulnerable release is Release 220.127.116.11.
Access Points Managed by Catalyst 9800 Wireless Controller or Embedded
Wireless Controller (EWC) on Catalyst Access Points
Cisco Catalyst 9800 Wireless First Fixed Release
Controller Software Release
16.12 and earlier Not vulnerable.
17.2 Migrate to a fixed release. ^1
17.3 IOS XE Access Point Service Pack
17.4 and later Not vulnerable.
1. The first vulnerable release is Release 17.2.1.
2. The first fixed release for this vulnerability is Release 17.3.4.
However, in order to fix this vulnerability and CSCvz08781 , the
recommendation is to upgrade to Release 17.3.4 and install the IOS XE
Access Point Service Pack 17.03.04.CSCvz17868.
Exploitation and Public Announcements
o The Cisco Product Security Incident Response Team (PSIRT) is not aware of
any public announcements or malicious use of the vulnerability that is
described in this advisory.
o This vulnerability was found during the resolution of a Cisco TAC support
Cisco Security Vulnerability Policy
o To learn about Cisco security vulnerability disclosure policies and
publications, see the Security Vulnerability Policy . This document also
contains instructions for obtaining fixed software and receiving security
vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2021-SEP-22 |
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