Headline
CVE-2021-34720: Cisco Security Advisory: Cisco IOS XR Software IP Service Level Agreements and Two-Way Active Measurement Protocol Denial of Service Vulnerability
A vulnerability in the IP Service Level Agreements (IP SLA) responder and Two-Way Active Measurement Protocol (TWAMP) features of Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause device packet memory to become exhausted or cause the IP SLA process to crash, resulting in a denial of service (DoS) condition. This vulnerability exists because socket creation failures are mishandled during the IP SLA and TWAMP processes. An attacker could exploit this vulnerability by sending specific IP SLA or TWAMP packets to an affected device. A successful exploit could allow the attacker to exhaust the packet memory, which will impact other processes, such as routing protocols, or crash the IP SLA process.
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.htmlAdditionally, 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 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
In the following table, the left column lists Cisco software release trains. The center column indicates which specific releases are affected by this vulnerability. The right column indicates the first fixed release.
Cisco IOS XR Software Release
Affected Releases
First Fixed Release for This Vulnerability
5.3 and earlier
All
Migrate to a fixed release.
6.0
All
Migrate to a fixed release.
6.1
All
Migrate to a fixed release.
6.2
6.2.1, 6.2.2
6.2.3
6.3
6.3.1
6.3.2, 6.3.3
6.4
Not vulnerable.
Not vulnerable.
6.5
6.5.2, 6.5.3
Migrate to a fixed release.
6.6
All
Migrate to a fixed release.
6.7
All
Fixed in 6.7.4 for ip sla responder configurations. ip sla responder twamp configurations are vulnerable; migrate to a fixed release.
7.0
All
Migrate to a fixed release.
7.1
All
Migrate to a fixed release.
7.2
All
7.2.2
7.3 and later
Not affected.
Not affected.
Cisco has released the following SMUs to address this vulnerability. Customers who require SMUs for platforms or releases that are not listed are advised to contact their support organization.
The SMUs in the following table address Cisco Bug ID CSCvw32825 (for ip sla responder configurations).
Cisco IOS XR Software Release
Platform
SMU Name
6.3.3
ASR9K-PX
asr9k-px-6.3.3.CSCvw32825
6.4.2
ASR9K-X64
asr9k-x64-6.4.2.CSCvw32825
6.5.3
ASR9K-PX
asr9k-px-6.5.3.CSCvw32825
6.6.3
ASR9K-PX
asr9k-px-6.6.3.CSCvw32825
ASR9K-X64
asr9k-x64-6.6.3.CSCvw32825
NCS5500
ncs5500-6.6.3.CSCvw32825
6.7.3
ASR9K-PX
asr9k-px-6.7.3.CSCvw32825
7.1.2
NCS540
ncs540-7.1.2.CSCvw32825
NCS560
ncs560-7.1.2.CSCvw32825
NCS5500
ncs5500-7.1.2.CSCvw32825
7.1.3
ASR9K-X64
asr9k-x64-7.1.3.CSCvw32825
The SMUs in the following table address Cisco Bug ID CSCvw61840 (for ip sla responder twamp configurations).
Cisco IOS XR Software Release
Platform
SMU Name
6.3.3
ASR9K-PX
asr9k-px-6.3.3.CSCvw61840
6.5.3
NCS5500
ncs5500-6.5.3.CSCvw61840
6.6.3
ASR9K-PX
asr9k-px-6.6.3.CSCvw61840
ASR9K-X64
asr9k-x64-6.6.3.CSCvw61840
7.1.3
ASR9K-X64
asr9k-x64-7.1.3.CSCvw61840
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.