A vulnerability in the WebVPN login process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause increased CPU utilization on an affected device. The vulnerability is due to excessive processing load for existing WebVPN login operations. An attacker could exploit this vulnerability by sending multiple WebVPN login requests to the device. A successful exploit could allow the attacker to increase CPU load on the device, resulting in a denial of service (DoS) condition. 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: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-sd-cpu-dos
A vulnerability in the WebVPN login process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause increased CPU utilization on an affected device.
The vulnerability is due to excessive processing load for existing WebVPN login operations. An attacker could exploit this vulnerability by sending multiple WebVPN login requests to the device. A successful exploit could allow the attacker to increase CPU load on the device, resulting in a denial of service (DoS) condition.
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:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-sd-cpu-dos
This vulnerability affects the following Cisco products that are running Cisco ASA Software or FTD Software when configured for WebVPN:
1ASA 5500 Series Adaptive Security Appliances other than the ASA 5505 have reached the end-of-support milestone and are no longer evaluated for security vulnerabilities.
For information about which Cisco ASA Software and FTD Software releases are vulnerable, see the Fixed Software section of this advisory.
To determine if the WebVPN service is enabled on a device, administrators can use the show running-config webvpn privileged EXEC command and refer to the output of the command. The following example shows the output of the command for a device that has the WebVPN service enabled:
Vulmon
ciscoasa# show running-config webvpn
. . . webvpn enable interface_name . . .
To determine which Cisco ASA Software release is running on a device, administrators can log in to the device, use the show version | include Version command in the CLI, and refer to the output of the command. The following example shows the output of the command for a device that is running Cisco ASA Software Release 9.9.2.18:
ciscoasa# show version | include Version
Cisco Adaptive Security Appliance Software Version 9.9.2.18
Device Manager Version 7.4(1)
.
.
.
If a device is managed by using Cisco Adaptive Security Device Manager (ASDM), administrators can also determine which release is running on a device by referring to the release information in the table that appears in the Cisco ASDM login window or the Device Dashboard tab of the Cisco ASDM Home pane.
To determine which Cisco FTD Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and refer to the output of the command. The following example shows the output of the command for a device that is running Cisco FTD Software Release 6.2.0:
> show version
---------------------[ ftd ]---------------------
Model : Cisco ASA5525-X Threat Defense (75) Version 6.2.0 (Build 362)
UUID : 2849ba3c-ecb8-11e6-98ca-b9fc2975893c
Rules update version : 2017-03-15-001-vrt
VDB version : 279
----------------------------------------------------
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
During active exploitation of this vulnerability, administrators may notice increased CPU usage by the Unicorn Proxy Thread process. This can be checked by issuing the show processes cpu-usage non-zero command at the CLI and reviewing the statistics for the Unicorn Proxy Thread process.
It should be noted that the previous output is an example. Administrators would need to compare the output values from their device to baseline values from normal device operation.ciscoasa# show processes cpu-usage non-zero
Hardware: ASA5516
Cisco Adaptive Security Appliance Software Version 9.8(2)38
ASLR enabled, text region 7f313ea71000-7f3142d61bb4
PC Thread 5Sec 1Min 5Min Process
0x00007f3140f35888 0x00002aaacfaa8b20 7.7% 5.0% 3.0% Unicorn Proxy Thread
- - 9.5% 1.9% 0.8% DATAPATH-0-2044
- - 3.6% 1.4% 0.8% DATAPATH-1-2045
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 software license:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.html
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 and Alerts page, to determine exposure and a complete upgrade solution.
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 providers.
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/en/us/support/web/tsd-cisco-worldwide-contacts.html
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 upgrade.
Customers are advised to upgrade to an appropriate release as indicated in the applicable table in this section. To ensure a complete upgrade solution, customers should consider that this advisory is part of a collection that includes the following advisories:
In the following table(s), the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.
Cisco ASA Software
| Cisco ASA Software Release | Recommended Release for This Vulnerability | Recommended Release for All the Vulnerabilities Described in the Collection of Advisories |
|---|---|---|
| Prior to 9.41 | 9.4.4.34 | 9.4.4.34 |
| 9.4 | 9.4.4.34 | 9.4.4.34 |
| 9.51 | 9.6.4.25 | 9.6.4.25 |
| 9.6 | 9.6.4.25 | 9.6.4.25 |
| 9.7 | 9.8.4 |
9.8.4 |
| 9.8 | 9.8.4 | 9.8.4 |
| 9.9 | 9.9.2.50 | 9.9.2.50 |
| 9.10 | Not vulnerable |
9.10.1.17 |
| 9.12 | Not vulnerable |
Not vulnerable |
Cisco FTD Software
| Cisco Firepower and FMC Software | Recommended Release for This Vulnerability | Recommended Release for All the Vulnerabilities Described in the Collection of Advisories |
|---|---|---|
| 6.0 |
6.2.3.12 | 6.2.3.12 |
| 6.0.1 | 6.2.3.12 | 6.2.3.12 |
| 6.1.0 | 6.2.3.12 |
6.2.3.12 |
| 6.2.0 | 6.2.3.12 |
6.2.3.12 |
| 6.2.1 | 6.2.3.12 | 6.2.3.12 |
| 6.2.2 | 6.2.3.12 |
6.2.3.12 |
| 6.2.3 |
6.2.3.12 | 6.2.3.12 |
| 6.3.0 | Not vulnerable |
6.3.0.3 |
| 6.4.0 | Not vulnerable | Not vulnerable |
To upgrade to a fixed release of Cisco FTD Software, customers can do one of the following:
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.
Cisco would like to thank Jason Moulder of Pratum for reporting this vulnerability.
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 |
|---|---|---|---|---|
| 1.1 | Updated the FTD fixed releases table to indicate that FTD Software Release 6.3.0.3 is available. | Fixed Software | Final | 2019-May-02 |
| 1.0 | Initial public release. | - | Final | 2019-May-01 |
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