Were you able to obtain any additional information about exactly what type of packets (and sequence) does this? It would make the ACL a lot cleaner. :-) -Jeremy -----Original Message----- From: Johnson, April [mailto:apjohnsonat_private] Sent: Wednesday, July 16, 2003 10:06 PM To: incidentsat_private Subject: Cisco IOS Denial of Service that affects most Cisco IOS routers- requires power cycle to recover For those with a CCO login: http://www.cisco.com/en/US/customer/products/hw/routers/ps341/products_s ecurity_advisory09186a00801a34c2.shtml Document ID: 44020 Revision 1.0 For Public Release 2003 July 17 at 0:00 UTC (GMT) ------------------------------------------------------------------------ -------- ------------------------------------------------------------------------ -------- Contents Summary Affected Products Details Impact Software Versions and Fixes Obtaining Fixed Software Workarounds Exploitation and Public Announcements Status of This Notice: INTERIM Distribution Revision History Cisco Security Procedures ------------------------------------------------------------------------ -------- Summary Cisco routers and switches running Cisco IOS(r) software and configured to process Internet Protocol version 4 (IPv4) packets are vulnerable to a Denial of Service (DoS) attack. A rare sequence of crafted IPv4 packets sent directly to the device may cause the input interface to stop processing traffic once the input queue is full. No authentication is required to process the inbound packet. Processing of IPv4 packets is enabled by default. Devices running only IP version 6 (IPv6) are not affected. A workaround is available. Cisco has made software available, free of charge, to correct the problem. This advisory is available at http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml. Affected Products This issue affects all Cisco devices running Cisco IOS software and configured to process Internet Protocol version 4 (IPv4) packets. Cisco devices which do not run Cisco IOS software are not affected. Devices which run only Internet Protocol version 6 (IPv6) are not affected. Details Cisco routers are configured to process and accept Internet Protocol version 4 (IPv4) packets by default. A rare, specially crafted sequence of IPv4 packets which is handled by the processor on a Cisco IOS device may force the device to incorrectly flag the input queue on an interface as full, which will cause the router to stop processing inbound traffic on that interface. This can cause routing protocols to drop due to dead timers. On Ethernet interfaces, Address Resolution Protocol (ARP) times out after a default time of four hours, and no traffic can be processed. The device must be rebooted to clear the input queue on the interface, and will not reload without user intervention. The attack may be repeated on all interfaces causing the router to be remotely inaccessible. A workaround is available, and is documented in the Workarounds section. The following two Cisco vulnerabilities are documented in DDTS. CSCea02355 (registered customers only) affects all Cisco routers running Cisco IOS software. CSCdz71127 (registered customers only) was introduced by an earlier code revision. Any version of software which has the fix for CSCdx02283 (registered customers only) is vulnerable. Registered customers can find more details using the Bug Toolkit at http://www.cisco.com/cgi-bin/Support/Bugtool/launch_bugtool.pl (registered customers only) . To identify a blocked input interface, use the show interfaces command and look for the Input Queue line. If the current size (in this case, 76) is larger than the maximum size (75), the input queue is blocked. Router#show interface ethernet 0/0 Ethernet0/0 is up, line protocol is up Hardware is AmdP2, address is 0050.500e.f1e0 (bia 0050.500e.f1e0) Internet address is 172.16.1.9/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:41, output 00:00:07, output hang never Last clearing of "show interface" counters 00:07:18 Input queue: 76/75/1091/0 (size/max/drops/flushes); Total output drops: 0 ^^^^^^^^^^^^^^ ---> blocked Impact A device receiving these specifically crafted IPv4 packets will force the inbound interface to stop processing traffic. The device may stop processing packets destined to the router, including routing protocol packets and ARP packets. No alarms will be triggered, nor will the router reload to correct itself. This issue can affect all Cisco devices running Cisco IOS software. This vulnerability may be exercised repeatedly resulting in loss of availability until a workaround has been applied or the device has been upgraded to a fixed version of code. Software Versions and Fixes Each row of the table 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 and the anticipated date of availability for each are listed in the Rebuild, Interim, and Maintenance columns. In some cases, no rebuild of a particular release is planned; this is marked with the label "Not scheduled." A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label). When selecting a release, keep in mind the following definitions: Maintenance Most heavily tested and highly recommended release of any label in a given row of the table. Rebuild Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific vulnerability. Although it receives less testing, it contains only the minimal changes necessary to effect the repair. Cisco has made available several rebuilds of mainline trains to address this vulnerability, but strongly recommends running only the latest maintenance release on mainline trains. Interim Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco Technical Assistance Center (TAC). 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 TAC for assistance, as shown in the section following this table. Train Description of Image or Platform Availability of Fixed Releases 11.x-based Releases Rebuild Interim Maintenance 11.1CA 11.1(36)CA4** 11.2 11.2(26e)** 11.2P 11.2(26)P5** 11.3 Not scheduled 11.3T Not scheduled 12.0-based Releases Rebuild Interim Maintenance 12.0 General Deployment release for all platforms 12.0(26) 12.0DA xDSL support: 6100, 6200 Migrate to 12.2DA; 12.2(10)DA2 - Aug-15-2003, 12.2(12)DA3 - Aug-22-2003: Engineering Specials available on request. 12.0DB Early Deployment 6400 UAC for NSP Migrate to 12.3(1a) 12.0DC Early Deployment 6400 UAC for NRP Migrate to 12.3(1a) 12.0S Core/ISP support: GSR, RSP, c7200, c10k 12.0(24)S2, 12.0(23)S3, 12.0(22)S5, 12.0(21)S7, 12.0(19)S4, 12.0(18)S7, 12.0(17)S7, 12.0(16)S10, 12.0(15)S7, 12.0(14)S8, 12.0(13)S8, 12.0(12)S4, 12.0(10)S8 12.0(25)S 12.0SC Cable/broadband ISP: uBR7200 Migrate to 12.1(19)EC 12.0SL 10000ESR: c10k Migrate to 12.0(23)S3, **12.0(17)SL9 - Jul-15-2003 12.0SP Early Deployment Migrate to 12.0(22)S5 12.0ST Early Deployment release for Core/ISP support: GSR, RSP, c7200 12.0(21)ST7, 12.0(20)ST6, 12.0(19)ST6, 12.0(17)ST8 12.0SX Early Deployment Migrate to 12.0(22)S5 12.0SY Early Deployment Migrate to 12.0(23)S3 12.0SZ Early Deployment Migrate to 12.0(23)S3 12.0T Early Deployment 12.0(7)T3** 12.0W5 85xx ls1010 12.0(26)W5(28) c5atm 12.0(24)W5(26a) Cat4232 and Cat2948G-L3 12.0(25)W5(27) C6MSM,C5rsfc, C5rsm Engineering Special available on request C3620, C3640, C4500, C7200, RSP 12.0WC Early deployment 2900XL-LRE,2900XL/3500XL; 2950 release 12.0(05)WC8 12.0WT Early deployment Catalyst switches: cat4840g Engineering Special Available upon request 12.0X(l) Short-lived Early Deployment Releases All 12.0X(any letter) releases have migrated to either 12.0T or 12.1 unless otherwise documented in the X release technical notes pertaining to the specific release. Please check migration paths for all 12.0X releases. 12.1-based Releases Rebuild Interim Maintenance 12.1 General Deployment release for all platforms 12.1(18.4) 12.1(19) 12.1AA Migrate to 12.2 12.1AX Catalyst 3750 12.1(14)EA1 - Engineering special available upon request 12.1AY Catalyst 2940 12.1(13)AY 12.1DA 6160 platform Migrate to 12.2DA 12.1DB 6400 UAC Migrate to 12.3(1a) 12.1DC 6400 UAC Migrate to 12.3(1a) 12.1E Core Enterprise support - c7200, Catalyst 6000, RSP 12.1(8b)E14 12.1(13)E7 12.1(14)E4 **12.1(12c)E7 12.1(11b)E12- Aug-4-2003 12.1(6)E12 12.1(19)E 12.1EA 12.1(4)EA 12.1(6)EA 12.1(8)EA 12.1(9)EA 12.1(11)EA 12.1(12c)EA 12.1(13)EA Migrate to 12.1(13)EA1c 12.1EB LS1010 12.1(14)EB 12.1EC Early Deployment 12.1(19)EC (scheduled last week of July) 12.1EV Early Deployment 12.1(12c)EV 12.1EW Early Deployment Cat4000 L3 12.1(13)EW,12.1(19)EW 12.1EX Early Deployment 12.1(13)EX2 12.1EY 12.1(14)E4 12.1YJ 12.1(14)EA1 - Jul-28-2003 12.1T Early Deployment 12.1(5)T15** 12.1X(l) 12.1X releases generally migrate to 12.1T, 12.2 or 12.2T as specified below. Please refer to specific train Technical notes for documented migration path. 12.1XA Short-lived Early Deployment Release Migrate to 12.1(5)T15 12.1XC 12.1XD 12.1XH 12.1XI Short-lived Early Deployment Releases Migrate to12.2(17) 12.1XB 12.1XF 12.1XG 12.1XJ 12.1XL 12.1XP 12.1XR 12.1XT 12.1YB 12.1YC 12.1YD 12.1YH Short-lived Early Deployment Releases Migrate to 12.2(15)T5 12.1XM 12.1XQ 12.1XV Short-lived Early Deployment Releases Migrate to 12.2(2)XB11 12.1XU Short-lived Early Deployment Release Migrate to 12.2(4)T6 12.1YE 12.1YF 12.1YI Short-lived Early Deployment Releases Migrate to 12.2(2)YC 12.2-based Releases Rebuild Interim Maintenance 12.2 General Deployment (GD) candidate for all platforms 12.2(16a), 12.2(12e), 12.2(10d) 12.2(17) 12.2B 12.2(2)B-12.2(4)B7 12.3(1a) 12.2(4)B8-12.2(16)B 12.2(16)B1 12.2BC Early Deployment Release 12.2(15)BC1 (Scheduled end of July) 12.2BW Early Deployment for use with 7200, 7400, and 7411 platforms Migrate to 12.3(1a) 12.2BX Broadband/Leased line 12.2(16)BX 12.2BZ Early Deployment Release 12.2(15)BZ1 12.2CX Early Deployment Release Migrate to 12.1(15)BC1 12.2CY Early Deployment Release Migrate to 12.1(15)BC1 12.2DA Early Deployment Release 12.2(10)DA2 - Jul-15-2003, 12.2(12)DA3 - Aug-22-2003 Engineering Special available on request 12.2DD Early Deployment Release Migrate to 12.3(1a) 12.2DX Early Deployment Release Migrate to 12.3(1a) 12.2JA Cisco Aironet hardware platforms: Introduction of Access Point feature in IOS, Cisco 1100 Series Access Point (802.11b) 12.2(11)JA 12.2MB Specific Technology ED for 2600 7500 (GPRS/PDSN/GGSN 2600/7200/7500) 12.2(4)MB12 12.2MC Early Deployment: IP RAN 12.2(13)MC1 CCO: 7/24/03 12.2MX 12.2(8)YD 12.2S Core/ISP support: GSR, RSP, c7200 12.2(14)S1 12.2(16.5)S 12.2SX IOS Support for C6500 Supervisor 3 12.2(14)SX1 12.2SY VPN feature release for c6k/76xx VPN service module 12.2(14)SY1, 12.2(8)YD 12.2SZ 7304 Platform 12.2(14)SZ2 12.2T New Technology Early Deployment (ED) release for all platforms 12.2(15)T4/5,12.2(13)T5, 12.2(11)T9,12.2(8)T10, 12.2(4)T6 12.2(16.5)T No more maintenance trains for 12.2T are planned. Please migrate to the latest 12.3 Mainline release. 12.2X(l) 12.2Y(l) Short-lived Early Deployment Releases Many short-lived releases migrate to the same train; the trains below this point until the following section are not grouped by strict alphabetical order, but are grouped by migration path. Please review documented migration paths for your trains. 12.2XA Short-lived Early Deployment Releases Migrate to 12.2(11)T9 12.2XS 12.2(2)XB11 12.2XD 12.2XE 12.2XH 12.2XI 12.2XJ 12.2XK 12.2XL 12.2XM 12.2XQ 12.2XU 12.2XW 12.2YA 12.2YB 12.2YC 12.2YF 12.2YG 12.2YH 12.2YJ 12.2YT Short-lived Early Deployment Releases Migrate to 12.2(15)T5 12.2YN Short-lived Early Deployment Release Migrate to 12.2(13)ZH 12.2YO Short-lived Early Deployment Release Migrate to 12.2(14)SY1 available Aug-4-2003: Engineering Special available on request 12.2XB Early Deployment Release with continuing support 12.2(2)XB11 12.2XC Short-lived Early Deployment Release Migrate to 12.2(16)B1 12.2XF Short-lived Early Deployment Release uBR10000 Migrate to 12.2(15)BC1 12.2XG Short-lived Early Deployment Release Migrate to 12.2(8)T10 12.2XN 12.2XT Short-lived Early Deployment Releases Migrate to 12.2(11)T9 12.2YD Short-lived Early Deployment Release Migrate to 12.2(8)YY 12.2YP Short-lived Early Deployment Release **12.2(11)YP1 12.2YK Migrate to 12.2(13)ZC 12.2YL 12.2YM 12.2YU 12.2YV Short-lived Early Deployment Releases Migrate to 12.2(13)ZH 12.2YQ 12.2YR Short-lived Early Deployment Releases Migrate to 12.2(15)ZL 12.2YS Short-lived Early Deployment Release 12.2(15)YS/1.2(1) 12.2YW Short-lived Early Deployment Release 12.2(8)YW2 12.2YX Short-lived Early Deployment Release Crypto for 7100/7200 12.2(11)YX1 12.2YY Short lived Early Deployment Releases IOS support for General Packet Radio Service 12.2(8)YY3 12.2YZ Short-lived Early Deployment Release 12.2(11)YZ2 12.2ZA Short-lived Early Deployment Release 12.2(14)ZA2 12.2ZB Short-lived Early Deployment Release 12.2(8)ZB7 12.2ZC Short-lived Early Deployment Release 12.2(13)ZC 12.2ZD Short-lived Early Deployment Release Not Scheduled 12.2ZE Short-lived Early Deployment Release 12.3(1a) 12.2ZF Short-lived Early Deployment Release Not Vulnerable 12.2ZG Short-lived Early Deployment Release Not Vulnerable 12.2ZH Short-lived Early Deployment Release Not Vulnerable 12.2ZJ Short-lived Early Deployment Release 12.2(15)ZJ1 12.2ZL Short-lived Early Deployment Release Not Vulnerable 12.3-based Releases NOT VULNERABLE Notes: ** Marked versions of code are not available on CCO. Please contact the Cisco TAC and request the specific images you need posted. Obtaining Fixed Software Customers with contracts should obtain upgraded software free of charge through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on the Cisco worldwide website at http://www.cisco.com/tacpage/sw-center/sw-ios.html. 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 assistance with obtaining the free software upgrade(s). 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: tacat_private Please 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. Please do not contact either "psirtat_private" or "security-alertat_private" for software upgrades. See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers, instructions, and e-mail addresses for use in various languages. Workarounds AFTER APPLYING THE WORKAROUND the input queue depth may be raised with the hold-queue <new value> in interface command -- the default size is 75. This will allow traffic flow on the interface until the device can be reloaded. Cisco recommends that all IOS devices which process IPv4 packets be configured to block traffic directed to the router from any unauthorized source with the use of Access Control Lists (ACLs). This can be done at multiple locations, and it is recommended that you review all methods and use the combination which fits your network best. Legitimate traffic is defined as management protocols such as telnet, snmp or ssh, and configured routing protocols from explicitly allowed peers. All other traffic destined to the device should be blocked at the input interface. Traffic entering the network should also be carefully evaluated and filtered at the network edge if destined to an infrastructure device. Although network service providers must often allow unknown traffic to transit their network, it is not necessary to allow that same traffic destined to their network infrastructure. Several white papers have been written to assist in deploying these recommended security best practices. ACLs can have performance impact on certain platforms, so care should be taken when applying the recommended workarounds. Receive ACLs For distributed platforms, receive path access lists may be an option starting in Cisco IOS software versions 12.0(21)S2 for the c12000 and 12.0(24)S for the c7500. The receive access lists protect the device from harmful traffic before the traffic can impact the route processor. The CPU load is distributed to the line card processors and helps mitigate load on the main route processor. 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/customer/707/racl.html Infrastructure ACLs 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. The white paper entitled "GSR: Receive Access Control Lists" presents guidelines and recommended deployment techniques for infrastructure protection ACLs: http://www.cisco.com/warp/customer/707/iacl.html Transit ACLs The two techniques described above protect infrastructure devices. This IP protocol ACL can also be used to filter transit traffic passing through a network. The ACL will need to permit all protocols used by end users, not just those destined to routers. Since end users can often run a wide array of protocols, often unexpected or uncommon protocols, these protocol requirements must be well understood prior to deploying this ACL. This access-list is applied inbound on edge facing interfaces. For complete protection this access-list needs to be implemented on the edge router. For basic TCP/UCP and ICMP, the following ACL will provide protection: access-list 101 permit tcp any any access-list 101 permit udp any any access-list 101 permit icmp any any access-list 101 permit gre any any /* GRE tunnel if required */ access-list 101 permit esp any any /* IPSec ESP if required */ access-list 101 permit ah any any /* IPSec AH if required */ access-list 101 deny ip any any The last statement of the Transit ACL should be a deny any any for IP traffic. Prior to deploying ACLs that filter transit traffic, a classification ACL can be used to help identify required permit statements. A classification ACL is an ACL that permits a series of protocols. Displaying access-list entry hit counters helps determine required protocols: entries with zero packets counted are likely not required. Classification access-lists are detailed in the above link for infrastructure access-lists. Exploitation and Public Announcements The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory. If PSIRT becomes aware of any sign of public announcement of the crafted packet, or there is any sign of exploitation of this vulnerability, a follow-up announcement will be sent to our standard distribution list immediately with further details to assist network administrators in mitigation. Status of This Notice: INTERIM This is an INTERIM notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this advisory unless there is some material change in the facts. Should there be a significant change in the facts, Cisco will update this advisory. Distribution This notice will be posted on the Cisco worldwide website at http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml at 21:00 GMT on July 17th, 2003. In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and will be posted to the following e-mail and Usenet news recipients at the public release date and time: cust-security-announceat_private bugtraqat_private full-disclosureat_private first-teamsat_private (includes CERT/CC) ciscoat_private cisco-nspat_private nanogat_private sanogat_private comp.dcom.sys.cisco Various internal Cisco mailing lists Future updates of this advisory, if any, will be placed on the Cisco worldwide web server. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History Revision 1.0 17-July-2003 0:00 GMT Initial 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 the Cisco worldwide website at http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco security notices. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt. ------------------------------------------------------------------------ -------- This notice is Copyright 2003 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, and include all date and version information. ------------------------------------------------------------------------ -------- ------------------------------------------------------------------------ -------- Updated: Jul 16, 2003 Document ID: 44020 ------------------------------------------------------------------------ -------- Customer Search: Site To SearchSearch All Cisco.comProducts & ServicesCisco RoutersCisco 7200 Series Routers BUSINESS INDUSTRIES & SOLUTIONS | NETWORKING SOLUTIONS & PROVISIONED SERVICES | PRODUCTS & SERVICES | TECHNOLOGIES | ORDERING | TECHNICAL SUPPORT | LEARNING & EVENTS | PARTNERS & RESELLERS | ABOUT CISCO Home | Logged In | Profile | Contacts & Feedback | Help | Site Map (c) 1992-2003 Cisco Systems, Inc. All rights reserved. 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