Cisco Security Advisory
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CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the Virtual Shell (VSH) session management for Cisco NX-OS Software could allow an authenticated, remote attacker to cause a VSH process to fail to delete upon termination. This can lead to a build-up of VSH processes that overtime can deplete system memory. When there is no system memory available, this can cause unexpected system behaviors and crashes.
The vulnerability is due to the VSH process not being properly deleted when a remote management connection to the device is disconnected. An attacker could exploit this vulnerability by repeatedly performing a remote management connection to the device and terminating the connection in an unexpected manner. A successful exploit could allow the attacker to cause the VSH processes to fail to delete, which can lead to a system-wide denial of service (DoS) condition. The attacker must have valid user credentials to log in to the device using the remote management connection.
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:
This advisory is part of the August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication, which includes five Cisco Security Advisories that describe five vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-nxos-memleak-dos
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Vulnerable Products
This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco NX-OS Software:
- MDS 9000 Series Multilayer Switches
- Nexus 3000 Series Switches
- Nexus 3500 Platform Switches
- Nexus 3600 Platform Switches
- Nexus 5500 Platform Switches
- Nexus 5600 Platform Switches
- Nexus 6000 Series Switches
- Nexus 7000 Series Switches
- Nexus 7700 Series Switches
- Nexus 9000 Series Switches in standalone NX-OS mode
- Nexus 9500 R-Series Switching Platform
- UCS 6200 Series Fabric Interconnects
- UCS 6300 Series Fabric Interconnects
For information about which Cisco NX-OS Software releases are vulnerable, see the Fixed Software section of this advisory.
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 2100 Series
- Firepower 4100 Series
- Firepower 9300 Security Appliances
- Nexus 1000 Virtual Edge for VMware vSphere
- Nexus 1000V Switch for Microsoft Hyper-V
- Nexus 1000V Switch for VMware vSphere
- Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
- UCS 6400 Series Fabric Interconnects
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The most common example of a remote management protocol is SSH but any management protocol including S/FTP, S/COPY and others to the management interface could trigger this vulnerability.
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Exploitation of this vulnerability can result in several different indicators of compromise on an affected device.
1. Exploitation of this vulnerability can result in a system memory leak due to the build-up of zombie VSH processes that were not terminated correctly. Administrators can view the process list using the show process NX-OS CLI command, as in the following example:
# show processes PID State PC Start_cnt TTY Process ----- ----- -------- ----------- ---- ------------- 1574 S f537a3c 1 - vsh 2063 S f537a3c 1 - vsh . . . 4308 S f537a3c 1 - vsh 4690 S f537a3c 1 - vsh 4733 S f537a3c 1 - vsh 5081 S f537a3c 1 - vsh 5949 S f537a3c 1 - vsh 6118 S f537a3c 1 - vsh 6723 S f537a3c 1 - vsh 7315 S f537a3c 1 - vsh 9841 S f537a3c 1 - vsh 12866 S f537a3c 1 - vsh 13465 S f537a3c 1 - vsh 14836 S f537a3c 1 - vsh 15568 S f537a3c 1 - vsh 18289 S f537a3c 1 - vsh 18580 S f537a3c 1 - vsh 18601 S f537a3c 1 - vsh 19254 S f537a3c 1 - vsh 19782 S f537a3c 1 - vsh 20367 S f537a3c 1 - vsh 20517 S f537a3c 1 - vsh 20931 S f537a3c 1 - vsh 21753 S f537a3c 1 - vsh 22728 S f537a3c 1 - vsh 23544 S f537a3c 1 - vsh 23947 S f537a3c 1 - vsh 24825 S f537a3c 1 - vsh 25139 S f537a3c 1 - vsh 25862 S f537a3c 1 - vsh 26172 S f537a3c 1 - vsh 26334 S f537a3c 1 - vsh 26691 S f537a3c 1 - vsh 27303 S f537a3c 1 - vsh 28750 S f537a3c 1 - vsh2. Exploitation of this vulnerability can result in the following error message when a user has a remote connection on the device:
Error: Too many open files in system
3. Exploitation of this vulnerability could cause an affected device to reload and generate a core file. Because the core file is the end result of the system memory leak, the actual process to crash can be different each time. To view the device core files, administrators can use the show core command in the NX-OS CLI. Contact the Cisco Technical Assistance Center (TAC) to review the core file and determine whether the device has been compromised by exploitation of this vulnerability.
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There are no workarounds that address this vulnerability.
Mitigation for Cisco NX-OS Software—Configure a VTY Access Class
On some platforms that are running Cisco NX-OS Software, it is possible to limit exposure of an affected device by creating a vty access control list (ACL) on the device and configuring the ACL to permit only known, trusted devices to connect to the device via Telnet and Secure Shell (SSH).
This mitigation is not available on some platforms that are running Cisco NX-OS and should be used only where applicable.
There is no Cisco UCS mitigation that addresses this vulnerability.
The ACL in this example is for IPv4. This vulnerability can also be exploited against IPv6 interfaces. If the NX-OS device is configured for IPv6, the same ACL should be configured for the IPv6 address range.
The following example shows an ACL that permits access to vtys from the 192.168.1.0/24 netblock and the single IP address 172.16.1.2 while denying access from all other addresses:
ip access-list vtyacl 10 permit tcp 192.168.1.0/24 172.16.1.2/32 line vty access-class vtyacl in
For more information about restricting traffic to vtys, see the Cisco Nexus 7000 Series NX-OS Security Configuration Guide. It is considered a best practice for an NX-OS device to have a vty ACL configured. Refer to the Cisco Guide to Securing Cisco NX-OS Software Devices for additional information about hardening Cisco NX-OS devices.
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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.htmlAdditionally, 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.htmlCustomers 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 help ensure a complete upgrade solution, customers should consider that this advisory is part of a bundled publication. The following page provides a complete list of bundle advisories: Cisco Event Response: August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.
In the following table(s), the left column lists releases of Cisco FXOS Software or Cisco NX-OS Software. 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 all the vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.
MDS 9000 Series Multilayer Switches: CSCvn50393
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories 5.2
6.2(27)
6.2(29) 6.2
6.2(27)
6.2(29) 7.3 8.4(1) 8.4(1)
8.1
8.4(1)
8.4(1)
8.2 8.4(1)
8.4(1)
8.3
8.4(1)
8.4(1)
8.4 Not vulnerable
Not vulnerable
Nexus 3000 Series Switches and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvi15409
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 7.0(3)I4
7.0(3)I4(9)
7.0(3)I4(9) 7.0(3)I4 7.0(3)I4(9)
7.0(3)I4(9) 7.0(3)I7 7.0(3)I7(4)
7.0(3)I7(6)
9.2 Not vulnerable
9.2(3) 9.3 Not vulnerable Not vulnerable
Nexus 3500 Platform Switches: CSCvi15409
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories 6.0(2)A
6.0(2)A8(11)
6.0(2)A8(11)
7.0(3)I7 7.0(3)I7(4)
7.0(3)I7(6) 9.2 Not vulnerable
9.2(3) 9.3 Not vulnerable Not vulnerable
Nexus 3600 Platform Switches and Nexus 9500 R-Series Switching Platform: CSCvi15409
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories 7.0(3)
9.2(1)
9.2(3)
9.2 Not vulnerable
9.2(3)
9.4 Not vulnerable Not vulnerable
Nexus 5500, 5600, and 6000 Series Switches: CSCvn50446
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 7.1
7.1(5)N1(1b)
7.1(5)N1(1b)
7.1 7.1(5)N1(1b)
7.1(5)N1(1b)
7.3 7.3(5)N1(1)
7.3(5)N1(1)
Nexus 7000 and 7700 Series Switches: CSCvn50443
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 6.2
6.2(22) 6.2(22) 6.2
6.2(22) 6.2(22) 7.2 7.3(4)D1(1)
7.3(4)D1(1) 7.3 7.3(4)D1(1)
7.3(4)D1(1) 8.0 8.2(3)
8.2(3)
8.1 8.2(3)
8.2(3)
8.2 8.2(3)
8.2(3)
8.3 8.4(1)
8.4(1) 8.4 Not vulnerable Not vulnerable
UCS 6200 and 6300 Series Fabric Interconnects: CSCvn52167
Cisco NX-OS Software Release First Fixed Release for This Vulnerability
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories Earlier than 3.2
3.2(3k)
3.2(3l)
3.2
3.2(3k)
3.2(3l)
4.0
4.0(2e)
4.0(4e)
Additional Resources
For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, administrators can refer to the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.
For help determining the best Cisco NX-OS Software release for Cisco UCS, refer to the Recommended Releases documents in the release notes for the device.Cisco MDS Series Switches
Cisco Nexus 1000V for VMware Switch
Cisco Nexus 3000 Series and 3500 Series Switches
Cisco Nexus 5000 Series Switches
Cisco Nexus 5500 Platform Switches
Cisco Nexus 6000 Series Switches
Cisco Nexus 7000 Series Switches
Cisco Nexus 9000 Series Switches
Cisco Nexus 9000 Series ACI-Mode Switches
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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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Show LessVersion Description Section Status Date 1.1 Updated the MDS and UCS fixed release tables. Fixed Software Final 2019-October-08 1.0 Initial public release. — Final 2019-August-28
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