A vulnerability in the UDP broadcast forwarding function of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on the affected device. The vulnerability is due to improper handling of UDP broadcast packets that are forwarded to an IPv4 helper address. An attacker could exploit this vulnerability by sending multiple UDP broadcast packets to the affected device. An exploit could allow the attacker to cause a buffer leak on the affected device, eventually resulting in a DoS condition requiring manual intervention to recover. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-iosxr
RP/0/RSP0/CPU0:Router# show running-config | include ipv4 helper-address
Building configuration...
ipv4 helper-address vrf default 192.0.2.1
RP/0/RSP0/CPU0:ASR9001#show version Wed Jan 24 01:32:32.751 EST Cisco IOS XR Software, Version 5.3.4[Default] Copyright (c) 2017 by Cisco Systems, Inc. ROM: System Bootstrap, Version 2.04(20140227:092320) [ASR9K ROMMON], ASR9001 uptime is 6 hours, 17 minutes System image file is "bootflash:disk0/asr9k-os-mbi-5.3.4.sp4-1.0.0/0x100000/mbiasr9k-rp.vm" cisco ASR9K Series (P4040) processor with 8388608K bytes of memory. P4040 processor at 1500MHz, Revision 2.0 ASR-9001 Chassis 2 Management Ethernet 8 TenGigE 20 GigabitEthernet 8 DWDM controller(s) 8 WANPHY controller(s) 44 GigabitEthernet/IEEE 802.3 interface(s) 219k bytes of non-volatile configuration memory. 2880M bytes of hard disk. 3932144k bytes of disk0: (Sector size 512 bytes). Configuration register on node 0/RSP0/CPU0 is 0x2102
RP/0/RSP0/CPU0:Router#show redundancy Redundancy information for node 0/RSP0/CPU0: ========================================== Node 0/RSP0/CPU0 is in ACTIVE role . . .
The following example shows the output of the show spp buffer location 0/RSP0/CPU0 CLI command on an affected device:
RP/0/RSP0/CPU0:Router#show spp buffer location 0/RSP0/CPU0 SPP Buffer Analysis PID Buffers 0 15065 225413 41108 Total Buffers in use: 49138 Owned by clients/spp (of which plugins): 41108/8030 (0) . . .
A continuous increase of the Owned by clients buffers could be an indication of a buffer leak.
The number of free buffers can be calculated by subtracting the number of Owned by SPP buffers from the number of buffers associated with PID 0. When the number of free buffers is reduced to 8192 or fewer, the affected device might be starting to drop control plane packets. In the previous example, the number of buffers associated with PID 0 is 15065 and the number of Owned by SPP buffers is 8030, so the number of free buffers is 15065 - 8030 = 7035.For a final confirmation on whether this message does indicate exploitation of this issue, please contact your support organization.RP/0/RSP0/CPU0:Feb 23 17:25:11.697 : netio[340]: %PKT_INFRA-spp-4-PKT_ALLOC_FAIL : Failed to allocate 1 packets for sending
There are no workarounds that address this vulnerability.
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:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.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 be upgraded 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:
https://www.cisco.com/c/en/us/support/web/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
This vulnerability has been corrected in Cisco IOS XR Software Release 6.3.2 and later.
Software maintenance upgrades (SMUs) for Cisco Aggregation Services Router (ASR) 9000 Series have also been made available that address this vulnerability.
| IOS XR Release | SMU ID | ASR 9000 SMU Name |
| 5.3.4 | AA14136 |
asr9k-px-5.3.4.CSCvi35625.tar 1 |
| 6.1.4 | AA14137 |
asr9k-px-6.1.4.CSCvi35625.tar |
| 6.2.3 | AA14138 |
asr9k-px-6.2.3.CSCvi35625.tar |
Customers using a Cisco IOS XR platform other than ASR 9000 Series Routers, or running a Cisco IOS XR Software Release for which no SMU is listed in the previous table, are advised to upgrade the IOS XR Software or open a support case to evaluate upgrade options.
Cisco IOS XR Software can be downloaded from the Software Center on Cisco.com by navigating to Downloads Home > Products > Routers > Service Provider Edge Routers or Service Provider Core Routers, selecting the appropriate product, and selecting IOS XR Software.
The SMUs for Cisco ASR 9000 Series Routers can be downloaded from the Software Center on Cisco.com by navigating to Downloads Home > Products > Routers > Service Provider Edge Routers > ASR 9000 Series Aggregation Services Routers > ASR 9xxx Router > Software on Chassis > IOS XR Software Maintenance Upgrades (SMU).
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.
This vulnerability was found during the resolution of a Cisco TAC support case.
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.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.0 | Initial public release. | - | Final | 2018-April-18 |
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