Summary

• A vulnerability in the Deterministic Random Bit Generator (DRBG), also known as Pseudorandom Number Generator (PRNG), used in Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a cryptographic collision, enabling the attacker to discover the private key of an affected device.
  
  The vulnerability is due to insufficient entropy in the DRBG when generating cryptographic keys. An attacker could exploit this vulnerability by generating a large number of cryptographic keys on an affected device and looking for collisions with target devices. A successful exploit could allow the attacker to impersonate an affected target device or to decrypt traffic secured by an affected key that is sent to or from an affected target device.

  Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-asa-ftd-entropy

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products that are running Cisco ASA Software Releases 9.8 or 9.9 or FTD Software Releases 6.2.1, 6.2.2, or 6.2.3:

  • 3000 Series Industrial Security Appliances (ISAs)
  • Adaptive Security Appliance (ASA) 5500-X Series with FirePOWER Services
  • Adaptive Security Virtual Appliance (ASAv)
  • Firepower 4100 Series
  • Firepower 9300 ASA Security Module
  • Firepower Threat Defense Virtual

  Note: Devices running other releases of Cisco ASA Software or FTD Software may also be vulnerable if they are configured with at least one of the following:

  • A Trustpoint that is based on an RSA or ECDSA key pair that has been generated while running an affected release
  • An RSA key pair for use with SSH Access that has been generated while running an affected release

  If no Trustpoint is configured and no RSA key pair for use with SSH Access is present, a device is vulnerable only while running an affected release.

  For information about which Cisco ASA Software and FTD Software releases are vulnerable, see the Fixed Software section of this advisory.

  ASA Software

  In the following table, the left column lists the Cisco ASA features that are potentially vulnerable. The right column indicates the basic configuration for the feature from the show running-config CLI command, if it can be determined.

  Cisco ASA Feature	Possible Vulnerable Configuration
  Adaptive Security Device Manager (ASDM)1	http server enable <port> http <remote_ip_address> <remote_subnet_mask> <interface_name>
  AnyConnect SSL VPN	webvpn  enable <interface_name>
  Cisco Security Manager1	http server enable <port> http <remote_ip_address> <remote_subnet_mask> <interface_name>
  Clientless SSL VPN (WebVPN)	webvpn  enable <interface_name>
  IKEv1 VPN (Remote Access and LAN-to-LAN) using Certificate-based Authentication	crypto ikev1 enable <interface_name> crypto ikev1 policy <priority>  authentication rsa-sig tunnel-group <tunnel_group_name> ipsec-attributes  trust-point <trustpoint_name>
  IKEv2 VPN (Remote Access and LAN-to-LAN) using Certificate-based Authentication	crypto ikev2 enable <interface_name> tunnel-group <tunnel_group_name> ipsec-attributes  ikev2 remote-authentication certificate  ikev2 local-authentication certificate <trustpoint_name>
  Local Certificate Authority (CA)	crypto ca server  no shutdown
  Mobile Device Manager (MDM) Proxy	mdm-proxy  enable <interface_name>
  Mobile User Security (MUS)	webvpn  mus password <password>  mus server enable port <port #>  mus <address> <mask> <interface_name>
  Proxy Bypass	webvpn  proxy-bypass
  REST API1	rest-api image disk0:/<image name> rest-api agent
  SSH Access2	ssh <remote_ip_address> <remote_subnet_mask> <interface_name>

  ¹ ASDM, CSM, and REST API services are accessible only from an IP address in the configured http command range.
  ² SSH service is accessible only from an IP address in the configured ssh command range.
  

  FTD Software

  In the following table, the left column lists the Cisco FTD features that are potentially vulnerable. The right column indicates the basic configuration for the feature from the show running-config CLI command, if it can be determined.

  Cisco FTD Feature	Possible Vulnerable Configuration
  AnyConnect SSL VPN1,2	webvpn  enable <interface_name
  Clientless SSL VPN (WebVPN)2	webvpn  enable <interface_name>
  HTTP Service enabled3,4	http server enable <port #> http <remote_ip_address> <remote_subnet_mask> <interface_name>
  IKEv1 VPN (Remote Access and LAN-to-LAN) using Certificate-based Authentication1,2	crypto ikev1 enable <interface_name> crypto ikev1 policy <priority>  authentication rsa-sig tunnel-group <tunnel_group_name> ipsec-attributes  trust-point <trustpoint_name>
  IKEv2 VPN (Remote Access and LAN-to-LAN) using Certificate-based Authentication1,2	crypto ikev2 enable <interface_name> tunnel-group <tunnel_group_name> ipsec-attributes  ikev2 remote-authentication certificate  ikev2 local-authentication certificate <trustpoint_name>
  SSH Service5	ssh <remote_ip_address> <remote_subnet_mask> <interface_name>

  ¹ Remote Access VPN features are enabled via Devices > VPN > Remote Access in the Cisco FMC or via Device > Remote Access VPN in Cisco Firepower Device Manager (FDM).
  ² The Clientless SSL VPN feature is not officially supported but can be enabled via FlexConfig.
  ³ The HTTP feature is enabled via Firepower Threat Defense Platform Settings > HTTP in the Cisco Firepower Management Console (FMC).
  ⁴ HTTP service is accessible only from an IP address in the configured http command range.
  ⁵ SSH is accessible only from an IP address in the configured ssh command range.
  

  Determining the Cisco ASA Software Release

  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.

  Determining the Cisco FTD Software Release

  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
  ----------------------------------------------------

  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 ASA Software or FTD Software running on the following platforms:

  • ASA 1000V Cloud Firewall
  • ASA 5505 Adaptive Security Appliance¹
  • ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Firepower 2100 Series

  ¹ ASA 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.

Workarounds

• To avoid the use of potentially weak cryptographic keys, administrators can generate a key pair and a corresponding certificate on a trusted device outside of the Cisco ASA or FTD device and then import the base 64 encoded PKCS #12 file containing the keys and certificate(s) to the Cisco ASA or FTD device using the crypto ca import <trust-point-name> pkcs12 <passphrase> command in global configuration mode.

  See the ASA 8.x: Renew and Install the SSL Certificate with ASDM tech note for further details, including steps for how to accomplish this task via the Cisco Adaptive Security Device Manager (ASDM).

Fixed Software

• 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

  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:

  • cisco-sa-20190501-asa-csrf: Cisco Adaptive Security Appliance Software Cross-Site Request Forgery Vulnerability
  • cisco-sa-20190501-asa-frpwrtd-dos: Cisco Adaptive Security Appliance Software and Cisco Firepower Threat Defense Software TCP Timer Handling Denial of Service Vulnerability
  • cisco-sa-20190501-asa-ftd-dos: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN Denial of Service Vulnerability
  • cisco-sa-20190501-asa-ftd-entropy: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Low-Entropy Keys Vulnerability
  • cisco-sa-20190501-asa-ftd-ike-dos: Cisco Adaptive Security Appliance Software and Cisco Firepower Threat Defense Software MOBIKE Denial of Service Vulnerability
  • cisco-sa-20190501-asaftd-saml-vpn: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software VPN SAML Authentication Bypass Vulnerability
  • cisco-sa-20190501-asa-ipsec-dos: Cisco Adaptive Security Appliance Software IPsec Denial of Service Vulnerability
  • cisco-sa-20190501-firepower-dos: Cisco Firepower Threat Defense Software TCP Ingress Handler Denial of Service Vulnerability
  • cisco-sa-20190501-frpwr-dos: Cisco Firepower Threat Defense Software Packet Processing Denial of Service Vulnerability
  • cisco-sa-20190501-frpwr-smb-snort: Cisco Firepower Threat Defense Software SMB Protocol Preprocessor Detection Engine Denial of Service Vulnerabilities
  • cisco-sa-20190501-sd-cpu-dos: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN Denial of Service Vulnerability

  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.

  Note: After upgrading to a fixed release, administrators must re-generate all RSA and ECDSA key pairs that were generated on an affected device while running a vulnerable release.

  Cisco ASA Software

  Cisco ASA Software Release	Recommended Release for This Vulnerability	Recommended Release for All Vulnerabilities Described in the Collection of Advisories
  Prior to 9.41	Not vulnerable	9.4.4.34
  9.4	Not vulnerable	9.4.4.34
  9.51	Not vulnerable	9.6.4.25
  9.6	Not vulnerable	9.6.4.25
  9.71	Not vulnerable	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

  ¹Cisco ASA Software releases prior to Release 9.4 and Cisco ASA Software Releases 9.5 and 9.7 have reached end of maintenance. Customers should migrate to a supported release that includes the fix for this vulnerability.

  Cisco FTD Software

  Cisco FTD Software Release	Recommended Release for This Vulnerability	Recommended Release for All Vulnerabilities Described in the Collection of Advisories
  6.0	Not vulnerable	6.2.3.12
  6.0.1	Not vulnerable	6.2.3.12
  6.1.0	Not vulnerable	6.2.3.12
  6.2.0	Not vulnerable	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	6.3.0.3	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:

  • 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.

Exploitation and Public Announcements

• 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.

Source

• Cisco would like to thank Greg Zaverucha of Microsoft for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-asa-ftd-entropy

Revision History

• 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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