CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the Secure Sockets Layer (SSL)/Transport Layer Security (TLS) handler of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to exhaust memory resources on the affected device, leading to a denial of service (DoS) condition.
The vulnerability is due to improper resource management for inbound SSL/TLS connections. An attacker could exploit this vulnerability by establishing multiple SSL/TLS connections with specific conditions to the affected device. A successful exploit could allow the attacker to exhaust the memory on the affected device, causing the device to stop accepting new SSL/TLS connections and resulting in a DoS condition for services on the device that process SSL/TLS traffic. Manual intervention is required to recover an affected device.
Cisco has released software updates that address the vulnerability described in this advisory. 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-asa-ssl-vpn-dos-qY7BHpjNThis advisory is part of the May 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication, which includes 12 Cisco Security Advisories that describe 12 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: May 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.
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Vulnerable Products
This vulnerability affects Cisco products if they are running a vulnerable release of Cisco ASA Software or FTD Software and have a feature enabled that causes the device to process SSL/TLS messages. These features include, but are not limited to, the following:
- AnyConnect SSL VPN
- Clientless SSL VPN
- HTTP server used for the management interface
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine Whether a Device Could Process SSL or TLS Messages
To verify whether a device that is running Cisco ASA Software or Cisco FTD Software could process SSL or TLS packets, use the show asp table socket | include SSL|DTLS command and verify that it returns output. When this command returns any output, the device is vulnerable. When this command returns empty output, the device is not affected by the vulnerability described in this advisory. The following example shows the output of the show asp table socket | include SSL|DTLS command from a device that is vulnerable:
ftd# show asp table socket | include SSL|DTLS
SSL 0005aa68 LISTEN x.x.x.x:443 0.0.0.0:*
SSL 002d9e38 LISTEN x.x.x.x:8443 0.0.0.0:*
DTLS 0018f7a8 LISTEN 10.0.0.250:443 0.0.0.0:*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 Cisco Firepower Management Center (FMC) Software.
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An affected device could stop accepting new SSL/TLS connections. Manual intervention would be required to recover the device. To do so, an administrator can log in to the CLI of the device and clear connections by using the following command:
clear conn all
If multiple connections are seen from specific IP addresses, the administrator can use the following command:
clear conn all address ip-address
Caution: The clear conn all command will clear all connections to or traversing through the device, regardless of whether they are SSL/TLS connections or whether they are improperly using system memory. Administrators are advised to use this command with care.
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There are no workarounds that address this vulnerability.
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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 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/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.
Fixed Releases
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 first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by any of the vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.
Cisco ASA Software
Cisco ASA Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 9.61 Migrate to a fixed release. Migrate to a fixed release. 9.6 9.6.4.40 Migrate to a fixed release. 9.71 Migrate to a fixed release. Migrate to a fixed release. 9.8 9.8.4.20 9.8.4.20 9.9 9.9.2.66 9.9.2.67 9.10 9.10.1.37 9.10.1.40 9.12 9.12.3.2 9.12.3.9 9.13 9.13.1.7 9.13.1.10 9.14 Not vulnerable. Not vulnerable. 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 FTD Software
Cisco FTD Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 6.1.01 Migrate to a fixed release. Migrate to a fixed release. 6.1.0 Migrate to a fixed release. Migrate to a fixed release. 6.2.0 Migrate to a fixed release. Migrate to a fixed release. 6.2.1 Migrate to a fixed release. Migrate to a fixed release. 6.2.2 Migrate to a fixed release.
Migrate to a fixed release. 6.2.3 6.2.3.16 (June 2020)
Cisco_FTD_Hotfix_DT-6.2.3.16-3.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_DT-6.2.3.16-3.sh.REL.tar
Cisco_FTD_SSP_Hotfix_DT-6.2.3.16-3.sh.REL.tar6.2.3.16 (June 2020)
Cisco_FTD_Hotfix_DT-6.2.3.16-3.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_DT-6.2.3.16-3.sh.REL.tar
Cisco_FTD_SSP_Hotfix_DT-6.2.3.16-3.sh.REL.tar6.3.0 6.3.0.6 (future release)
Cisco_FTD_Hotfix_AO-6.3.0.6-2.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_ AO-6.3.0.6-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_ AO-6.3.0.6-2.sh.REL.tar6.3.0.6 (future release)
Cisco_FTD_Hotfix_AO-6.3.0.6-2.sh.REL.tar
Cisco_FTD_SSP_FP2K_Hotfix_ AO-6.3.0.6-2.sh.REL.tar
Cisco_FTD_SSP_Hotfix_ AO-6.3.0.6-2.sh.REL.tar6.4.0 6.4.0.9 6.4.0.9 6.5.0 6.5.0.5 (future release)
Cisco_FTD_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_FP1K_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_FP2K_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_Hotfix_H-6.5.0.5-2.sh.REL.tar and later6.5.0.5 (future release)
Cisco_FTD_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_FP1K_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_FP2K_Hotfix_H-6.5.0.5-2.sh.REL.tar and later
Cisco_FTD_SSP_Hotfix_H-6.5.0.5-2.sh.REL.tar and later6.6.0 Not vulnerable. 6.6.0 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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This vulnerability was found during the resolution of a Cisco TAC support case.
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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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Version Description Section Status Date 1.2 Updated Hot Fixes for FTD releases 6.4.0 and 6.5.0. Fixed Releases Final 2020-MAY-15 1.1 Updated ASA Fixed Release table to indicate 9.10.1.40 as the correct fixed release instead of 9.10.1.39. Fixed Releases Final 2020-MAY-06 1.3 Updated fixed release information for FTD Release 6.4.0. Fixed Releases Final 2020-MAY-06 1.0 Initial public release. — Final 2020-MAY-06
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