[c-nsp] Cisco Security Advisory: Crafted TCP Packet Can Cause Denial of Service
Rick Kunkel
kunkel at w-link.net
Wed Feb 28 16:31:14 EST 2007
Hello all,
Has anyone heard of any cases of systems hit either by this exploit, or by
the other 2 or 3 that came out in this same clump of announcements?
It would seem that there'd be counters out there or something...
Thanks,
Rick Kunkel
On Wed, 24 Jan 2007, Cisco Systems Product Security Incident Response Team wrote:
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> Cisco Security Advisory: Crafted TCP Packet Can Cause Denial of
> Service
>
> Advisory ID: cisco-sa-20070124-crafted-tcp
>
> http://www.cisco.com/warp/public/707/cisco-sa-20070124-crafted-tcp.shtml
>
> Revision 1.0
>
> For Public Release 2007 January 24 1600 UTC (GMT)
>
> - ---------------------------------------------------------------------
>
> Summary
> =======
>
> The Cisco IOS Transmission Control Protocol (TCP) listener in certain
> versions of Cisco IOS software is vulnerable to a
> remotely-exploitable memory leak that may lead to a denial of service
> condition.
>
> This vulnerability only applies to traffic destined to the Cisco IOS
> device. Traffic transiting the Cisco IOS device will not trigger this
> vulnerability.
>
> Cisco has made free software available to address this vulnerability
> for affected customers.
>
> This issue is documented as Cisco bug ID CSCek37177.
>
> There are workarounds available to mitigate the effects of the
> vulnerability.
>
> This advisory is posted at
> http://www.cisco.com/warp/public/707/cisco-sa-20070124-crafted-tcp.shtml
>
> Affected Products
> =================
>
> Vulnerable Products
> +------------------
>
> This issue affects all Cisco devices running Cisco IOS software. To
> be affected, devices must be configured to process Internet Protocol
> version 4 (IPv4) packets and receive TCP packets. Devices which run
> only Internet Protocol version 6 (IPv6) are not affected.
>
> This vulnerability is present in all unfixed versions of Cisco IOS
> software, including versions 9.x, 10.x, 11.x and 12.x.
>
> 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". On the next line of
> output, the image name will be displayed between parentheses,
> 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 Cisco IOS
> release 12.2(14)S16 with an installed image name of C7200-IS-M:
>
> Cisco Internetwork Operating System Software
> IOS (tm) 7200 Software (C7200-IS-M), Version 12.2(14)S16, RELEASE SOFTWARE (fc1)
>
>
> The release train label is "12.2".
>
> The next example shows a product running IOS release 12.3(7)T12 with
> an image name of C7200-IK9S-M:
>
> Cisco IOS Software, 7200 Software (C7200-IK9S-M), Version 12.3(7)T12, RELEASE SOFTWARE (fc1)
>
>
> Additional information about Cisco IOS Banners is available at:
>
> http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_white_paper09186a008018305e.shtml#3
>
> Products Confirmed Not Vulnerable
> +--------------------------------
> Cisco products that do not run IOS are unaffected by this
> vulnerability.
>
> Cisco IOS-XR is not affected.
>
> No other Cisco products are currently known to be affected by this
> vulnerability.
>
> Details
> =======
>
> TCP is the transport layer protocol designed to provide
> connection-oriented, reliable delivery of a data stream. To
> accomplish this, TCP uses a mixture of flags to indicate state and
> sequence numbers to identify the order in which the packets are to be
> reassembled. TCP also provides a number, called an acknowledgement
> number, that is used to indicate the sequence number of the next
> packet expected. The full specification of the TCP protocol can be
> found at http://www.ietf.org/rfc/rfc0793.txt
>
> Cisco IOS devices that are configured to receive TCP packets are
> exposed to this issue. This Advisory does not apply to traffic that
> is transiting the device.
>
> Certain crafted packets destined to an IPv4 address assigned to a
> physical or virtual interface on a Cisco IOS device may cause the
> device to leak a small amount of memory. Over time, such a memory
> leak may lead to memory exhaustion and potentially degraded service.
>
> Although this is an issue with TCP, it is not required to complete
> the TCP 3-way handshake in order for the memory leak to be triggered.
> Therefore, TCP packets with a spoofed source address may trigger the
> leak.
>
> The following document contains additional information on how to
> identify if your router is suffering from a memory leak in Processor
> memory:
>
> http://www.cisco.com/warp/public/63/mallocfail.shtml#tshoot2
>
> Vulnerability Scoring Details
> =============================
>
> Cisco is providing scores for the vulnerabilities in this advisory
> based on the Common Vulnerability Scoring System (CVSS). 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.
>
> Cisco PSIRT will set the bias in all cases to normal. Customers are
> encouraged to apply the bias parameter when determining the
> environmental impact of a particular vulnerability.
>
> 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:
> http://intellishield.cisco.com/security/alertmanager/cvss
>
> Cisco Bug IDs:
>
> CSCek37177
>
> CVSS Base Score: 3.3
> Access Vector: Remote
> Access Complexity: Low
> Authentication: Not Required
> Confidentiality Impact: None
> Integrity Impact: None
> Availability Impact: Complete
> Impact Bias: Normal
>
> CVSS Temporal Score: 2.7
> Exploitability: Functional
> Remediation Level: Official Fix
> Report Confidence: Confirmed
>
> Impact
> ======
>
> Successful exploitation of the vulnerability may result in a small
> amount of processor memory to leak, which may lead to degraded
> service. This issue will not resolve over time, and will require a
> device reset to recover the leaked memory.
>
> This vulnerability only applies to traffic destined to the Cisco IOS
> device. Traffic transiting the device will not trigger this issue.
>
> Software Version 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
>
>
> Workarounds
> ===========
>
> Additional mitigations that can be deployed on Cisco devices within
> the network are available in the Cisco Applied Intelligence companion
> document for this advisory:
>
> http://www.cisco.com/warp/public/707/cisco-air-20070124-crafted-tcp.shtml
>
> Note: Configuring VTY access-class filters is not an effective
> mitigation strategy for this vulnerability.
>
> Infrastructure ACLs (iACL)
> +-------------------------
>
> Although it is often difficult to block traffic transiting your
> network, it is possible to identify traffic which 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 TCP services from trust hosts destined
> !--- to infrastructure addresses.
>
> access-list 150 permit tcp TRUSTED_HOSTS MASK INFRASTRUCTURE_ADDRESSES MASK
>
> !--- Deny TCP packets from all other sources destined to infrastructure addresses.
>
> access-list 150 deny tcp any INFRASTRUCTURE_ADDRESSES MASK
>
> !--- 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 entitled "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/warp/public/707/iacl.html
>
> Receive ACLs (rACL)
> +------------------
>
> For distributed platforms, Receive ACLs may be an option starting in
> Cisco IOS Software Versions 12.0(21)S2 for the 12000 (GSR), 12.0(24)S
> for the 7500, and 12.0(31)S for the 10720. The Receive ACL protects
> the device from harmful traffic before the traffic can impact the
> route processor. Receive ACLs are designed to only protect the device
> on which it is configured. On the 12000, transit traffic is never
> affected by a receive ACL. Because of this, the destination IP
> address "any" used in the example ACL entries below only refer to the
> router's own physical or virtual IP addresses. On the 7500 and 10720,
> transit traffic with IP options set will be subject to the Receive
> ACL and permitted or denied accordingly. Receive 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 white paper entitled "GSR:
> Receive Access Control Lists" will help you identify and allow
> legitimate traffic to your device and deny all unwanted packets:
> http://www.cisco.com/warp/public/707/racl.html
>
> The following is the receive path ACL written to permit this type of
> traffic from trusted hosts:
>
> !--- Permit tcp services from trusted hosts allowed to the RP.
>
> access-list 151 permit tcp TRUSTED_ADDRESSES MASK any
>
> !--- Deny tcp services from all other sources to the RP.
>
> access-list 151 deny tcp any any
>
> !--- Permit all other traffic to the RP.
>
> access-list 151 permit ip any any
>
> !--- Apply this access list to the 'receive' path.
>
> ip receive access-list 151
>
>
> Control Plane Policing (CoPP)
> +----------------------------
>
> The Control Plane Policing (CoPP) feature may be used to mitigate
> this vulnerability. In the following example, only TCP traffic from
> trusted hosts and with 'receive' destination IP addresses is
> permitted to reach the route processor (RP). All other 'transit' IP
> traffic is unaffected.
>
> It should be noted that 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
> access-list 152 permit tcp any any
> access-list 152 deny ip any any
> !
> class-map match-all permit-tcp-class
> match access-group 152
> !
> !
> policy-map permit-tcp-policy
> class permit-tcp-class
> drop
> !
> control-plane
> service-policy input permit-tcp-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.
>
> Please note that in the 12.2S and 12.0S Cisco IOS trains the
> policy-map syntax is different:
>
> policy-map permit-tcp-policy
> class class permit-tcp-class
> police 32000 1500 1500 conform-action drop exceed-action drop
>
>
> 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/products/sw/iosswrel/ps1838/products_white_paper09186a0080211f39.shtml
>
> Anti-spoofing
> +------------
>
> The Unicast Reverse Path Forwarding (Unicast RPF or uRPF) feature
> helps to mitigate problems that are caused by spoofed IP source
> addresses. It is available on Cisco routers and firewalls. For
> further details, please refer to:
>
> http://www.cisco.com/en/US/partner/products/ps6441/products_command_reference_chapter09186a00804ae49f.html#wp1229984
>
> By enabling Unicast Reverse Path Forwarding (uRPF), all spoofed
> packets will be dropped at the first device. To enable uRPF, use the
> following commands.
>
> router(config)# ip cef
> router(config)# interface interface #
> router(config-if)# ip verify unicast source reachable-via rx
>
> BGP and BTSH/GTSM
> +----------------
>
> Depending on your release of software, it may be possible to protect
> your BGP sessions from this memory leak. With the introduction of
> CSCee73956, Cisco IOS has improved support for BTSH (BGP TTL Security
> Hack) to reduce, if not eliminate a risk of a memory leak due to this
> vulnerability. This functionality is also known as GTSM (Generalized
> TTL Security Mechanism) and documented in RFC 3682. This section
> refers to GTSM as applied to eBGP sessions only.
>
> Releases of Cisco IOS that contain CSCee73956 are protected from this
> attack against the BGP port (TCP port 179) only. Other ports should
> be protected accordingly.
>
> BTSH is not supported for iBGP sessions. BTSH was first introduced in
> Cisco IOS in 12.0(27)S, 12.3(7)T and 12.2(25)S. Note that the BTSH
> feature prior to CSCee73956 will not protect against this
> vulnerability.
>
> For more information on BTSH, please see:
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123t/123t_7/gt_btsh.htm
>
> Obtaining Fixed Software
> ========================
>
> Cisco will make free software available to address this vulnerability
> for affected customers. This advisory will be updated as fixed
> software becomes available. 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 during our internal
> testing process.
>
> 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-20070124-crafted-tcp.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
> ================
>
> +---------------------------------------+
> | | | Initial |
> | 1.0 | 2007-January-24 | 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_vulnerability_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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