Cisco Security Advisory
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CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:X/RL:X/RC:X
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A vulnerability in the WebVPN feature 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 a specific WebVPN HTTP page request. An attacker could exploit this vulnerability by sending multiple WebVPN HTTP page load requests for a specific URL. A successful exploit could allow the attacker to increase CPU load on the device, resulting in a denial of service (DoS) condition, which could cause traffic to be delayed through the device.
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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191002-asa-ftd-dos
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Vulnerable Products
This vulnerability affects Cisco products running Cisco ASA Software or FTD Software when configured for WebVPN.
For information about which Cisco ASA Software and FTD Software releases are vulnerable, see the Fixed Software section of this advisory.Determine If WebVPN Is Enabled
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:
ciscoasa# show running-config webvpn
.
.
.
webvpn
enable interface_name
.
.
.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 the following Cisco products:
- Firepower Management Center (FMC)
- Firepower Management Center 1000
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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.
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-1-2045It should be noted that this output is an example. Administrators would need to compare the output values from their device(s) to baseline values from normal device operation.
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There are no workarounds that address this vulnerability.
It is possible that during active exploitation, an administrator could mitigate the attack by implementing an access control list (ACL) to block the incoming requests or perform rate limiting.
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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.
Fixed Releases
In the following table(s), the left column lists releases of Cisco ASA Software, Cisco FMC Software, or Cisco FTD Software. The right column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability.
Cisco ASA Software
1. Cisco ASA Software releases 9.5 and earlier, as well as Release 9.7, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.Cisco ASA Software Release First Fixed Release for This Vulnerability Earlier than 9.41 Migrate to a fixed release.
9.41 Migrate to a fixed release.
9.51 Migrate to a fixed release. 9.6 9.6.4.31 9.71 Migrate to a fixed release.
9.8 9.8.4.9 9.9 9.9.2.56 9.10 9.10.1.30
9.12 9.12.2.9
9.13 9.13.1
Cisco FTD Software
Cisco FTD Software Release First Fixed Release for This Vulnerability Earlier than 6.1.01 Migrate to a fixed release. 6.1.0 Migrate to a fixed release. 6.2.0 Migrate to a fixed release. 6.2.1 Migrate to a fixed release. 6.2.2 Migrate to a fixed release.
6.2.3 6.2.3.15 6.3.0 6.3.0.5 6.4.0 6.4.0.6 6.5.0 Not vulnerable. 1. Cisco FMC and FTD Software releases 6.0.1 and earlier have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.
To upgrade to a fixed release of Cisco FTD Software, customers can do one of the following:
- For devices that are managed by using Cisco Firepower Management Center (FMC), use the FMC interface to install the upgrade. After installation is complete, reapply the access control policy.
- For devices that are managed by using Cisco Firepower Device Manager (FDM), use the FDM interface to install the upgrade. After installation is complete, reapply the access control policy.
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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.
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Cisco would like to thank Qian Chen of Qihoo 360 Nirvan Team for reporting this vulnerability.
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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.
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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2019-October-02
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