Cisco Security Advisory
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CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X
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A privilege escalation vulnerability in the Secure Shell (SSH) subsystem in the StarOS operating system for Cisco ASR 5000 Series, ASR 5500 Series, ASR 5700 Series devices, and Cisco Virtualized Packet Core could allow an authenticated, remote attacker to gain unrestricted, root shell access.
The vulnerability is due to missing input validation of parameters passed during SSH or SFTP login. An attacker could exploit this vulnerability by providing crafted user input to the SSH or SFTP command-line interface (CLI) during SSH or SFTP login. An exploit could allow an authenticated attacker to gain root privileges access on the router.
Note: Only traffic directed to the affected system can be used to exploit this vulnerability. This vulnerability can be triggered via both IPv4 and IPv6 traffic. An established TCP connection toward port 22, the SSH default port, is needed to perform the attack. The attacker must have valid credentials to login to the system via SSH or SFTP.
Cisco has released software updates that address this vulnerability. Workarounds that mitigate this vulnerability are not available.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170315-asr
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Vulnerable Products
The following products have been confirmed to be vulnerable:
- Cisco ASR 5000/5500/5700 Series devices running StarOS after 17.7.0 and prior to 18.7.4, 19.5, and 20.2.3 with SSH configured are vulnerable.
- Cisco Virtualized Packet Core - Single Instance (VPC-SI) and Distributed Instance (VPC-DI) devices running StarOS prior to N4.2.7 (19.3.v7) and N4.7 (20.2.v0) with SSH configured are vulnerable.
Similarly, administrators can issue the show version command from the CLI to determine whether a vulnerable version of Cisco StarOS is running on a vPC-SI or vPC-DI instance. The following output is an example of a vPC instance that is running StarOS version N4.6 (20.1.v0):[local]ASR-2# show version
Friday August 12 13:17:31 AST 2016
Active Software:
Image Version: 19.2.1
Image Build Number: 62564
Image Description: Deployment_Build
Image Date: Thu Dec 31 20:13:39 EST 2015
Boot Image: /flash/asr5500-19.2.1.bin
To determine whether SSH is configured on Cisco StarOS or Cisco vPC software, administrators can issue the show configuration | grep sshd command from the CLI. In the following example, the presence of the server sshd line shows that the SSH server is enabled:[local]vPC-DI# show version
Active Software:
Image Version: 20.1.v0
Image Build Number: 64657
Image Description: Deployment_Build
Image Date: Wed Jul 27 18:46:53 EDT 2016
Boot Image: /flash/qvpc-di-20.1.v0.bin
[local]ASR-2# show configuration | grep sshd
server sshdProducts Confirmed Not Vulnerable
Cisco has confirmed that this vulnerability does not affect the following products:
- Cisco Elastic Services Controller (ESC)
- Cisco Ultra Automation Services (UAS)
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Successful exploitation of this vulnerability causes CLI logs to show a CLI session starting for the compromised user and the same CLI session ending within a few milliseconds. Administrators can view CLI logs by using the show logs facility cli command. In the following example, the user inspector exploited this vulnerability.
[local]ASR-2# show logs facility cli
2017-Feb-01+13:33:08.477 [cli 30005 info] [6/0/14607 <cli:6014607> _commands_cli.c:1775] [software internal system syslog] CLI session ended for Inspector inspector on device
2017-Feb-01+13:33:08.455 [cli 30004 info] [6/0/14607 <cli:6014607> cli_sess.c:127] [software internal system syslog] CLI session started for Inspector inspector on device from 10.X.X.X
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There are no workarounds that address this vulnerability.
Administrators can restrict access to the management interface, (for example, by applying an access control list (ACL)), to limit the attack surface.
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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:
http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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 upgrade 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:
http://www.cisco.com/en/US/support/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
In the following tables, the left column lists major releases of Cisco StarOS and Cisco vPC software, respectively. The right column indicates whether a major release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability.
StarOS for Cisco ASR 5000/5500/5700 Series RoutersCisco StarOS Major Release
First Fixed Release
17.7 and earlier
Not affected
18.0 18.7.4 19.0 19.5 20.0 20.2.3 21.0 Not affected
Cisco Virtualized Packet Core (vPC) Software
Cisco vPC Major Release
First Fixed Release
N4.0 (19.2)
Affected; migrate to N4.2.7 (19.3.v7) or later
N4.2 (19.3)
N4.2.7 (19.3.v7)
N4.5 (20.0)
Affected; migrate to N4.7 (20.2.v0) or later
N4.6 (20.1)
Affected; migrate to N4.7 (20.2.v0) or later
N4.7 (20.2)
Fixed
N5.0 (21.0)
Not affected
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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 internal security testing.
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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 2017-March-15
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