Summary

• A vulnerability in the Modbus preprocessor of the Snort detection engine could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

  This vulnerability is due to an integer overflow while processing Modbus traffic. An attacker could exploit this vulnerability by sending crafted Modbus traffic through an affected device. A successful exploit could allow the attacker to cause the Snort process to hang, causing traffic inspection to stop.

  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-snort-dos-9D3hJLuj

Affected Products

• Vulnerable Products

  This vulnerability affects all open source Snort project releases earlier than Release 2.9.19 and Release 3.1.11.0. For more information, see the Snort website.

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco software:

  • Cyber Vision Software
  • FirePOWER Services Software - All platforms
  • Firepower Threat Defense (FTD) Software - All platforms
  • Meraki MX Series Software

  Note: For FTD Software, Modbus inspection is enabled by default for the Security Over Connectivity and Max Detect Network Analysis Policies (NAP). For Cyber Vision Software and Meraki MX Series Software, Modbus inspection is enabled by default.

  This vulnerability affects the following Cisco products if they are running a release earlier than the first fixed release of Cisco Unified Threat Defense (UTD) Snort Intrusion Prevention System (IPS) Engine for Cisco IOS XE Software or Cisco UTD Engine for Cisco IOS XE SD-WAN Software:

  • 1000 Series Integrated Services Routers (ISRs)
  • 4000 Series Integrated Services Routers (ISRs)
  • Catalyst 8000V Edge Software
  • Catalyst 8200 Series Edge Platforms
  • Catalyst 8300 Series Edge Platforms
  • Catalyst 8500 Series Edge Platforms
  • Catalyst 8500L Series Edge Platforms
  • Cloud Services Routers 1000V
  • Integrated Services Virtual Routers (ISRv)

  Note: UTD is not installed on these devices by default.

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

  Determine Whether UTD is Enabled

  To determine whether UTD is enabled on a device, issue the show utd engine standard status command and check for a Yes under Running. The following output shows a device with UTD enabled:

  Router# show utd engine standard status 
  Engine version       : 1.0.19_SV2.9.16.1_XE17.3
  Profile              : Cloud-Low
  System memory        :
               Usage  : 6.00 %
               Status : Green
  Number of engines    : 1

  
  

  Engine        Running    Health     Reason    
  ===========================================
  Engine(#1):   Yes        Green      None
  =======================================================
  
  .
  .
  .

  If there is no output after issuing the command, the device is not affected.

  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:

  • Adaptive Security Appliance (ASA) Software
  • Firepower Management Center (FMC) Software

Details

• For the Meraki MX series devices, exploitation of this vulnerability results in the bypass of inspection services. This could result in malicious traffic not generating alerts and in turn reaching devices that are located behind the MX series device. For this reason, the Security Impact Rating (SIR) for Meraki MX devices is Medium.

  For Cyber Vision, exploitation of this vulnerability results in the bypass of Snort intrusion detection (IDS) services. This could result in malicious traffic not generating alerts. Deep packet inspection (DPI) and anomaly detection services are not impacted. For this reason, the SIR for Cyber Vision software is Medium.

Workarounds

• While there are no workarounds that address this vulnerability, for FTD Software that is managed by Firepower Management Center (FMC) the Modbus preprocessor can be disabled to mitigate the attack vector for this vulnerability.

  To disable a preprocessor in an FTD NAP for a device running Snort 2, see Preprocessor Configuration in a Network Analysis Policy Notes.

  To disable an inspector in an FTD NAP for a device running Snort 3, see Custom Network Analysis Policy Creation for Snort 3.

  For an FTD device managed by Firepower Device Manager (FDM), the device must be running Snort 3. For more information, see Configuring the Network Analysis Policy (Snort 3).

  If you need assistance implementing this mitigation, contact the Cisco Technical Assistance Center (TAC).

  While this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

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 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

  FTD and FirePOWER Services Software

  Cisco FTD and FirePOWER Services Software Release	First Fixed Release
  6.2.2 and earlier1	Migrate to a fixed release.
  6.2.3	Migrate to a fixed release.
  6.3.01	Migrate to a fixed release.
  6.4.0	6.4.0.13
  6.5.01	Migrate to a fixed release.
  6.6.0	6.6.5.1
  6.7.0	Migrate to a fixed release.
  7.0.0	7.0.1

  1. Cisco FMC and FTD Software releases 6.2.2 and earlier, as well as releases 6.3.0 and 6.5.0, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide.

  Cyber Vision Software

  Cisco Cyber Vision Software Release	First Fixed Release for This Vulnerability
  3.2 and earlier	Migrate to a fixed release.
  4.0	4.0.2

  Meraki MX Software

  Cisco Meraki MX Software Release	First Fixed Release
  MX14	Migrate to a fixed release.
  MX15	Migrate to a fixed release.
  MX16	16.16

  UTD Software

  Cisco UTD Software Release	First Fixed Release
  16.12	16.12.7
  17.3	17.3.5
  17.6	17.6.2
  17.7	Not vulnerable.

  Snort Software

  Cisco Snort Software Release	First Fixed Release
  2.x	2.9.19
  3.x	3.1.11.0

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

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 Uri Katz of Claroty Research for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-dos-9D3hJLuj

Revision History

• Version	Description	Section	Status	Date
  1.5	Updated Meraki fixed release.	Fixed Releases	Final	2022-APR-26
  1.4	Added FirePOWER Services Software.	Vulnerable Products, Fixed Software	Final	2022-FEB-04
  1.3	Clarified FTD policies that have Modbus enabled by default. Provided guidance on disabling Modbus preprocessor.	Vulnerable Products, Workarounds	Final	2022-JAN-26
  1.2	Updated the platforms that will receive a hotfix.	Fixed Software	Final	2022-JAN-26
  1.1	Updated affected releases and fixed releases for Snort software. Updated Cyber Vision product naming.	Affected Releases, Details, and Fixed Software	Final	2022-JAN-21
  1.0	Initial public release.	—	Final	2022-JAN-19

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