[nsp-sec] Cisco Security Advisory: Cisco IOS Secure Shell Denial ofService
Smith, Donald
Donald.Smith at qwest.com
Wed May 21 12:41:30 EDT 2008
The 2nd link doesn't work it is missing the L in shtml.
Security through obscurity WORKS against some worms and ssh bruteforce
tools:)
Donald.Smith at qwest.com giac
> -----Original Message-----
> From: nsp-security-bounces at puck.nether.net
> [mailto:nsp-security-bounces at puck.nether.net] On Behalf Of
> Cisco Systems Product Security Incident Response Team
> Sent: Wednesday, May 21, 2008 10:00 AM
> To: nsp-security at puck.nether.net
> Cc: psirt at cisco.com
> Subject: [nsp-sec] Cisco Security Advisory: Cisco IOS Secure
> Shell Denial ofService
>
> ----------- nsp-security Confidential --------
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Cisco Security Advisory: Cisco IOS Secure Shell Denial of Service
> Vulnerabilities
>
> Advisory ID: cisco-sa-20080521-ssh
>
> http://www.cisco.com/warp/public/707/cisco-sa-20080521-ssh.shtml
>
> Revision 1.0
>
> For Public Release 2008 May 21 1600 UTC (GMT)
>
> +--------------------------------------------------------------------
>
> Summary
> =======
>
> The Secure Shell server (SSH) implementation in Cisco IOS contains
> multiple vulnerabilities that allow unauthenticated users the ability
> to generate a spurious memory access error or, in certain cases,
> reload the device.
>
> The IOS SSH server is an optional service that is disabled by
> default, but its use is highly recommended as a security best
> practice for management of Cisco IOS devices. SSH can be configured
> as part of the AutoSecure feature in the initial configuration of IOS
> devices, AutoSecure run after initial configuration, or manually.
> Devices that are not configured to accept SSH connections are not
> affected by these vulnerabilities.
>
> Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-1159
> has been assigned to this vulnerability.
>
> This advisory is posted at
> http://www.cisco.com/warp/public/707/cisco-sa-20080521-ssh.shtm
>
> Affected Products
> =================
>
> Vulnerable Products
> +------------------
>
> Cisco devices running certain 12.4-based IOS releases and configured
> to be managed via SSH may be affected by this issue.
>
> The IOS secure shell server is disabled by default. To determine if
> SSH is enabled, use the show ip ssh command.
>
> Router#show ip ssh
> SSH Enabled - version 2.0
> Authentication timeout: 120 secs; Authentication retries: 3
>
> The previous output shows that SSH is enabled on this device and that
> the SSH protocol major version that is being supported is 2.0. If the
> text "SSH Disabled" is displayed, the device is not vulnerable.
> Possible values for the SSH protocol version reported by IOS are:
>
> * 1.5: only SSH protocol version 1 is enabled
> * 1.99: SSH protocol version 2 with SSH protocol version 1
> compatibility enabled
> * 2.0: only SSH protocol version 2 is enabled
>
> For more information about SSH versions in IOS, please check the
> following URL:
> http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide
> /gt_ssh2.html
>
> The SSH server is not available in all IOS images. Devices that do
> not support SSH are not vulnerable. Please consult the table of fixed
> software in the Software Version and Fixes section for the specific
> 12.4-based IOS releases that are affected.
>
> To determine the software running on a Cisco product, log in to the
> device and issue the show version command to display the system
> banner. Cisco IOS software will identify itself as "Internetwork
> Operating System Software" or simply "IOS". The image name will be
> displayed between parentheses on the next line of output followed by
> "Version" and the IOS release name. Other Cisco devices will not have
> the show version command or will give different output.
>
> The following example identifies a Cisco product running IOS release
> 12.4(17):
>
> Cisco IOS Software, C2600 Software
> (C2600-ADVENTERPRISEK9-M), Version 12.4(17),
> RELEASE SOFTWARE (fc1)
> Technical Support: http://www.cisco.com/techsupport
> Copyright (c) 1986-2007 by Cisco Systems, Inc.
> Compiled Fri 07-Sep-07 16:05 by prod_rel_team
>
> ROM: System Bootstrap, Version 12.2(8r) [cmong 8r],
> RELEASE SOFTWARE (fc1)
>
> Router uptime is 1 week, 5 hours, 5 minutes
> System returned to ROM by power-on
> System image file is "flash:c2600-adventerprisek9-mz.124-17.bin"
>
> Additional information about Cisco IOS release naming is available at
> http://www.cisco.com/warp/public/620/1.html
>
> Products Confirmed Not Vulnerable
> +--------------------------------
>
> Cisco devices that do not run IOS are not affected.
>
> Cisco IOS devices that do not have the SSH server feature enabled are
> not affected.
>
> IOS-XR images are not affected.
>
> The following IOS release trains are not affected:
>
> * 10-based releases
> * 11-based releases
> * 12.0-based releases
> * 12.1-based releases
> * 12.2-based releases
> * 12.3-based releases
>
> IOS releases prior to 12.4(7), 12.4(13d)JA, and 12.4(9)T are not
> affected by this vulnerability.
>
> No other Cisco products are currently known to be affected by these
> vulnerabilities.
>
> Details
> =======
>
> Secure shell (SSH) was developed as a secure replacement for the
> telnet, ftp, rlogin, rsh, and rcp protocols, which allow for the
> remote access of devices. The main difference between SSH and older
> protocols is that SSH provides strong authentication, guarantees
> confidentiality, and uses encrypted transactions.
>
> The server side of the SSH implementation in Cisco IOS contains
> multiple vulnerabilities that allow an unauthenticated user to
> generate a spurious memory access or, in certain cases, reload the
> device. If the attacker is able to reload the device, these
> vulnerabilities could be repeatedly exploited to cause an extended
> Denial of Service (DoS) condition.
>
> A device with the SSH server enabled is vulnerable.
>
> These vulnerabilities are documented in Cisco Bug IDs:
>
> * CSCsk42419 ( registered customers only)
> * CSCsk60020 ( registered customers only)
> * CSCsh51293 ( registered customers only)
>
> Vulnerability Scoring Details
> =============================
>
> Cisco is providing scores for the vulnerabilities in this advisory
> based on the Common Vulnerability Scoring System (CVSS). The CVSS
> scoring in this Security Advisory is done in accordance with CVSS
> version 2.0.
>
> Cisco will provide a base and temporal score. Customers can then
> compute environmental scores to assist in determining the impact of
> the vulnerability in individual networks.
>
> CVSS is a standards-based scoring method that conveys vulnerability
> severity and helps determine urgency and priority of response.
>
> Cisco has provided an FAQ to answer additional questions regarding
> CVSS at
>
> http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html
>
> Cisco has also provided a CVSS calculator to help compute the
> environmental impact for individual networks at
>
> http://intellishield.cisco.com/security/alertmanager/cvss
>
> * CSCsk42419 - SSHv2 spurious memory access
>
> CVSS Base Score - 7.8
> Access Vector - Network
> Access Complexity - Low
> Authentication - None
> Confidentiality Impact - None
> Integrity Impact - None
> Availability Impact - Complete
>
> CVSS Temporal Score - 6.4
> Exploitability - Functional
> Remediation Level - Official-Fix
> Report Confidence - Confirmed
>
> * CSCsk60020 - SSHv2 spurious memory access
>
> CVSS Base Score - 7.8
> Access Vector - Network
> Access Complexity - Low
> Authentication - None
> Confidentiality Impact - None
> Integrity Impact - None
> Availability Impact - Complete
>
> CVSS Temporal Score - 6.4
> Exploitability - Functional
> Remediation Level - Official-Fix
> Report Confidence - Confirmed
>
> * CSCsh51293 - Spurious memory access when SSH packets received
>
> CVSS Base Score - 7.8
> Access Vector - Network
> Access Complexity - Low
> Authentication - None
> Confidentiality Impact - None
> Integrity Impact - None
> Availability Impact - Complete
>
> CVSS Temporal Score - 6.4
> Exploitability - Functional
> Remediation Level - Official-Fix
> Report Confidence - Confirmed
>
> Impact
> ======
>
> Successful exploitation of these vulnerabilities may result in a
> spurious memory access or, in certain cases, reload the device
> potentially resulting in a DoS condition.
>
> Software Versions and Fixes
> ===========================
>
> When considering software upgrades, also consult
> http://www.cisco.com/go/psirt and any subsequent advisories to
> determine exposure and a complete upgrade solution.
>
> In all cases, customers should exercise caution to be certain the
> devices to be upgraded contain sufficient memory and that current
> hardware and software configurations will continue to be supported
> properly by the new release. If the information is not clear, contact
> the Cisco Technical Assistance Center ("TAC") or your contracted
> maintenance provider for assistance.
>
> Each row of the Cisco IOS software table (below) describes a release
> train and the platforms or products for which it is intended. If a
> given release train is vulnerable, then the earliest possible
> releases that contain the fix (the "First Fixed Release") and the
> anticipated date of availability for each are listed in the "Rebuild"
> and "Maintenance" columns. A device running a release in the given
> train that is earlier than the release in a specific column (less
> than the First Fixed Release) is known to be vulnerable. The release
> should be upgraded at least to the indicated release or a later
> version (greater than or equal to the First Fixed Release label).
>
> For more information on the terms "Rebuild" and "Maintenance,"
> consult the following URL:
> http://www.cisco.com/warp/public/620/1.html
>
> IOS releases prior to 12.4(7), 12.4(13d)JA, and 12.4(9)T are not
> affected by this vulnerability.
>
> +----------------------------------------+
> | Major | Availability of Repaired |
> | Release | Releases |
> |------------+---------------------------|
> | Affected | First Fixed | Recommended |
> | 12.0-Based | Release | Release |
> | Releases | | |
> |----------------------------------------|
> | There are no affected 12.0 based |
> | releases |
> |----------------------------------------|
> | Affected | First Fixed | Recommended |
> | 12.1-Based | Release | Release |
> | Releases | | |
> |----------------------------------------|
> | There are no affected 12.1 based |
> | releases |
> |----------------------------------------|
> | Affected | First Fixed | Recommended |
> | 12.2-Based | Release | Release |
> | Releases | | |
> |----------------------------------------|
> | There are no affected 12.2 based |
> | releases |
> |----------------------------------------|
> | Affected | First Fixed | Recommended |
> | 12.3-Based | Release | Release |
> | Releases | | |
> |----------------------------------------|
> | There are no affected 12.3 based |
> | releases |
> |----------------------------------------|
> | Affected | First Fixed | Recommended |
> | 12.4-Based | Release | Release |
> | Releases | | |
> |------------+-------------+-------------|
> | | 12.4(13f) | |
> | | | |
> | | 12.4(16b) | |
> | 12.4 | | 12.4(18b) |
> | | 12.4(17a) | |
> | | | |
> | | 12.4(18) | |
> |------------+-------------+-------------|
> | | Only 12.4 | |
> | | (13d)JA and | |
> | | 12.4(13d) | |
> | | JA1 are | |
> | 12.4JA | vulnerable, | 12.4(16b) |
> | | all other | JA3 |
> | | 12.4JA | |
> | | releases | |
> | | are not | |
> | | affected. | |
> |------------+-------------+-------------|
> | 12.4JK | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4JMA | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4JMB | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4JMC | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4JX | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4MD | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4MR | 12.4(16)MR2 | 12.4(16)MR |
> |------------+-------------+-------------|
> | 12.4SW | 12.4(15)SW1 | 12.4(15)SW1 |
> |------------+-------------+-------------|
> | | 12.4(9)T6 | |
> | | | |
> | | 12.4(11)T4 | |
> | 12.4T | | 12.4(15)T5 |
> | | 12.4(15)T2 | |
> | | | |
> | | 12.4(20)T | |
> |------------+-------------+-------------|
> | 12.4XA | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XB | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XC | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XD | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | | Vulnerable; | |
> | 12.4XE | first fixed | 12.4(15)T5 |
> | | in 12.4T | |
> |------------+-------------+-------------|
> | | Vulnerable; | |
> | 12.4XF | first fixed | 12.4(15)T5 |
> | | in 12.4T | |
> |------------+-------------+-------------|
> | 12.4XG | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | | Vulnerable; | |
> | 12.4XJ | first fixed | 12.4(15)T5 |
> | | in 12.4T | |
> |------------+-------------+-------------|
> | | Vulnerable; | |
> | 12.4XK | first fixed | 12.4(15)T5 |
> | | in 12.4T | |
> |------------+-------------+-------------|
> | 12.4XL | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XM | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XN | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XQ | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XT | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XV | Vulnerable; | |
> | | contact TAC | |
> |------------+-------------+-------------|
> | 12.4XW | 12.4(11)XW6 | 12.4(11)XW6 |
> |------------+-------------+-------------|
> | 12.4XY | Not | |
> | | Vulnerable | |
> |------------+-------------+-------------|
> | 12.4XZ | Not | |
> | | Vulnerable | |
> +----------------------------------------+
>
> Workarounds
> ===========
>
> If disabling the IOS SSH Server is not feasible, the following
> workarounds may be useful to some customers in their environments.
>
> Telnet
> +-----
>
> Telnet is not vulnerable to the issue described in this advisory and
> may be used as an insecure alternative to SSH. Telnet does not
> encrypt the authentication information or data; therefore, it should
> only be enabled for trusted local networks.
>
> VTY Access Class
> +---------------
>
> It is possible to limit the exposure of the Cisco device by applying
> a VTY access class to allow only known, trusted hosts to connect to
> the device via SSH.
>
> For more information on restricting traffic to VTYs, please consult:
> http://cisco.com/en/US/products/sw/iosswrel/ps1835/products_co
> mmand_reference_chapter09186a00800873c8.html#wp1017389
>
> The following example 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 anywhere else:
>
> Router(config)# access-list 1 permit 192.168.1.0 0.0.0.255
> Router(config)# access-list 1 permit host 172.16.1.2
> Router(config)# line vty 0 4
> Router(config-line)# access-class 1 in
>
> Different Cisco platforms support different numbers of terminal
> lines. Check your device's configuration to determine the correct
> number of terminal lines for your platform.
>
> Infrastructure ACLs (iACL)
> +-------------------------
>
> Although it is often difficult to block traffic transiting your
> network, it is possible to identify traffic that should never be
> allowed to target your infrastructure devices and block that traffic
> at the border of your network. Infrastructure ACLs are considered a
> network security best practice and should be considered as a
> long-term addition to good network security as well as a workaround
> for this specific vulnerability. The ACL example shown below should
> be included as part of the deployed infrastructure access-list, which
> will protect all devices with IP addresses in the infrastructure IP
> address range.
>
> A sample access list for devices running Cisco IOS is below:
>
>
> !--- Permit SSH services from trusted hosts destined
> !--- to infrastructure addresses.
> access-list 150 permit tcp TRUSTED_HOSTS MASK
> INFRASTRUCTURE_ADDRESSES MASK eq 22
> !--- Deny SSH packets from all other sources destined to
> infrastructure addresses.
> access-list 150 deny tcp any INFRASTRUCTURE_ADDRESSES MASK eq 22
> !--- Permit all other traffic to transit the device.
> access-list 150 permit IP any any
>
> interface serial 2/0
> ip access-group 150 in
>
> The white paper titled "Protecting Your Core: Infrastructure
> Protection Access Control Lists" presents guidelines and recommended
> deployment techniques for infrastructure protection access lists.
> This white paper can be obtained here:
> http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white
> _paper09186a00801a1a55.shtml
>
> Control Plane Policing (CoPP)
> +----------------------------
>
> The Control Plane Policing (CoPP) feature may be used to mitigate
> these vulnerabilities. In the following example, only SSH traffic
> from trusted hosts and with 'receive' destination IP addresses is
> permitted to reach the route processor (RP).
>
> Note: Dropping traffic from unknown or untrusted IP addresses may
> affect hosts with dynamically assigned IP addresses from connecting
> to the Cisco IOS device.
>
> access-list 152 deny tcp TRUSTED_ADDRESSES MASK any eq 22
> access-list 152 permit tcp any any eq 22
> !
> class-map match-all COPP-KNOWN-UNDESIRABLE
> match access-group 152
> !
> !
> policy-map COPP-INPUT-POLICY
> class COPP-KNOWN-UNDESIRABLE
> drop
> !
> control-plane
> service-policy input COPP-INPUT-POLICY
>
> In the above CoPP example, the ACL entries that match the exploit
> packets with the "permit" action result in these packets being
> discarded by the policy-map "drop" function, while packets that match
> the "deny" action are not affected by the policy-map drop function.
>
> CoPP is available in Cisco IOS release trains 12.0S, 12.2SX, 12.2S,
> 12.3T, 12.4, and 12.4T.
>
> Additional information on the configuration and use of the CoPP
> feature can be found at the following URL:
> http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6
> 586/ps6642/prod_white_paper0900aecd804fa16a.html
>
> Obtaining Fixed Software
> ========================
>
> Cisco has made free software available to address this vulnerability
> for affected customers. Prior to deploying software, customers should
> consult their maintenance provider or check the software for feature
> set compatibility and known issues specific to their environment.
>
> Customers may only install and expect support for the feature sets
> they have purchased. By installing, downloading, accessing or
> otherwise using such software upgrades, customers agree to be bound
> by the terms of Cisco's software license terms found at
> http://www.cisco.com/public/sw-license-agreement.html, or as
> otherwise set forth at Cisco.com Downloads at
> http://www.cisco.com/public/sw-center/sw-usingswc.shtml
>
> Do not contact either "psirt at cisco.com" or "security-alert at cisco.com"
> for software upgrades.
>
> Customers with Service Contracts
> +-------------------------------
>
> Customers with contracts should obtain upgraded software through
> their regular update channels. For most customers, this means that
> upgrades should be obtained through the Software Center on Cisco's
> worldwide website at http://www.cisco.com
>
> Customers using Third-party Support Organizations
> +------------------------------------------------
>
> Customers whose Cisco products are provided or maintained through
> prior or existing agreement with third-party support organizations
> such as Cisco Partners, authorized resellers, or service providers
> should contact that support organization for guidance and assistance
> with the appropriate course of action in regards to this advisory.
>
> The effectiveness of any workaround or fix is dependent on specific
> customer situations such as product mix, network topology, traffic
> behavior, and organizational mission. Due to the variety of affected
> products and releases, customers should consult with their service
> provider or support organization to ensure any applied workaround or
> fix is the most appropriate for use in the intended network before it
> is deployed.
>
> Customers without Service Contracts
> +----------------------------------
>
> Customers who purchase direct from Cisco but who do not hold a Cisco
> service contract and customers who purchase through third-party
> vendors but are unsuccessful at obtaining fixed software through
> their point of sale should get their upgrades by contacting the Cisco
> Technical Assistance Center (TAC). TAC contacts are as follows.
>
> * +1 800 553 2447 (toll free from within North America)
> * +1 408 526 7209 (toll call from anywhere in the world)
> * e-mail: tac at cisco.com
>
> Have your product serial number available and give the URL of this
> notice as evidence of your entitlement to a free upgrade. Free
> upgrades for non-contract customers must be requested through the
> TAC.
>
> Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
> for additional TAC contact information, including special localized
> telephone numbers and instructions and e-mail addresses for use in
> various languages.
>
> Exploitation and Public Announcements
> =====================================
>
> The Cisco PSIRT is not aware of any public announcements or malicious
> use of the vulnerability described in this advisory.
>
> This vulnerability was discovered by Cisco internal testing and
> customer service requests.
>
> Status of This Notice: FINAL
> ============================
>
> 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 stand-alone copy or Paraphrase of the text of this document that
> omits the distribution URL in the following section is an
> uncontrolled copy, and may lack important information or contain
> factual errors.
>
> Distribution
> ============
>
> This advisory is posted on Cisco's worldwide website at
> http://www.cisco.com/warp/public/707/cisco-sa-20080521-ssh.shtml
>
> In addition to worldwide web posting, a text version of this notice
> is clear-signed with the Cisco PSIRT PGP key and is posted to the
> following e-mail and Usenet news recipients.
>
> * cust-security-announce at cisco.com
> * first-teams at first.org
> * bugtraq at securityfocus.com
> * vulnwatch at vulnwatch.org
> * cisco at spot.colorado.edu
> * cisco-nsp at puck.nether.net
> * full-disclosure at lists.grok.org.uk
> * comp.dcom.sys.cisco at newsgate.cisco.com
>
> Future updates of this advisory, if any, will be placed on Cisco's
> worldwide website, but may or may not be actively announced on
> mailing lists or newsgroups. Users concerned about this problem are
> encouraged to check the above URL for any updates.
>
> Revision History
> ================
>
> +---------------------------------------+
> | Revision | | Initial |
> | 1.0 | 2008-May-21 | public |
> | | | release. |
> +---------------------------------------+
>
> Cisco Security Procedures
> =========================
>
> Complete information on reporting security vulnerabilities in Cisco
> products, obtaining assistance with security incidents, and
> registering to receive security information from Cisco, is available
> on Cisco's worldwide website at
> http://www.cisco.com/en/US/products/products_security_vulnerab
> ility_policy.html
> This includes instructions for press inquiries regarding Cisco
> security notices. All Cisco security advisories are available at
> http://www.cisco.com/go/psirt
>
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>
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