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AUSCERT External Security Bulletin Redistribution
ESB-2017.0692
Cisco StarOS SSH Privilege Escalation Vulnerability
16 March 2017
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco StarOS
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Root Compromise -- Existing Account
Resolution: Patch/Upgrade
CVE Names: CVE-2017-3819
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170315-asr
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Cisco Security Advisory
Cisco StarOS SSH Privilege Escalation Vulnerability
High
Advisory ID: cisco-sa-20170315-asr
First Published: 2017 March 15 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs:
CSCva65853
CVE-2017-3819
CWE-264
CVSS Score:
Base 8.8, Temporal 8.8
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
CVE-2017-3819
CWE-264
Summary
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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170315-asr
Affected Products
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.
To determine whether a vulnerable version of Cisco StarOS is running on ASR
5000/5500/5700 Series devices, administrators can issue the show version
command from the CLI. The following output is an example of a router that
is running StarOS version 19.2.1.
[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
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]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
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]ASR-2# show configuration | grep sshd
server sshd
Products 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)
No other Cisco products are currently known to be affected by this
vulnerability.
Indicators of Compromise
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
.
.
.
Workarounds
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.
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:
http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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 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.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 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 Routers
Cisco 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
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
This vulnerability was found during internal security testing.
Cisco Security Vulnerability Policy
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.
URL
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170315-asr
Revision History
Version Description Section Status Date
1.0 Initial public release. Final 2017-March-15
Legal Disclaimer
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND
OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT
OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES
THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information
or contain factual errors. The information in this document is intended for
end users of Cisco products.
Cisco Security Vulnerability Policy
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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