Pierluigi Paganini September 30, 2020

Cisco addressed two actively exploited DoS vulnerabilities that reside in the IOS XR software that runs on multiple carrier-grade routers.

Cisco addressed two high severity memory exhaustion DoS vulnerabilities that reside in the IOS XR Network OS that runs on multiple carrier-grade routers.

The company confirmed that both vulnerabilities are actively exploited in attacks in the wild.

At the end of August, Cisco warned that attackers are trying to exploit a high severity memory exhaustion denial-of-service (DoS) vulnerability (CVE-2020-3566) affecting the Cisco IOS XR Network OS that runs on carrier-grade routers.

Cisco IOS XR Network OS currently run on multiple router families, including NCS 540 & 560, NCS 5500, 8000, and ASR 9000 series routers.

This flaw affects any Cisco device that is running any release of Cisco IOS XR Software if an active interface is configured under multicast routing.

“A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to exhaust process memory of an affected device.” reads the advisory.

“On August 28, 2020, the Cisco Product Security Incident Response Team (PSIRT) became aware of attempted exploitation of this vulnerability in the wild.” 

The vulnerability is caused by insufficient queue management for Internet Group Management Protocol (IGMP) packets, it could be exploited by an attacker by sending crafted IGMP traffic to a vulnerable device.

A successful attack could cause memory exhaustion, resulting in instability of other processes, including interior and exterior routing protocols.

The advisory recommends users to run the show igmp interface command to determine if multicast routing is enabled on their device.

Running the command on IOS XR routers were multicast routing is not enabled will produce an empty output.  The following output shows a device with multicast routing enabled:

RP/0/0/CPU0:router# show igmp interface

Loopback0 is up, line protocol is up
  Internet address is 10.144.144.144/32
  IGMP is enabled on interface
  Current IGMP version is 3
  IGMP query interval is 60 seconds
  IGMP querier timeout is 125 seconds
  IGMP max query response time is 10 seconds
  Last member query response interval is 1 seconds
  IGMP activity: 3 joins, 0 leaves
  IGMP querying router is 10.144.144.144 (this system)
TenGigE0/4/0/0 is up, line protocol is up
  Internet address is 10.114.8.44/24
  IGMP is enabled on interface
  Current IGMP version is 3
  IGMP query interval is 60 seconds
  IGMP querier timeout is 125 seconds
  IGMP max query response time is 10 seconds
  Last member query response interval is 1 seconds
  IGMP activity: 9 joins, 4 leaves
  IGMP querying router is 10.114.8.11

At the time, Cisco only provided multiple mitigations, one of them consist of implementing a rate limiter to reduce the traffic rate and increase the time necessary for successful exploitation.

The IT giant has now released free Software Maintenance Upgrades (SMUs) to address the two vulnerabilities.

The advisory published by the company also includes the Indicators of Compromise (IoCs)

Pierluigi Paganini

(SecurityAffairs – hacking, Cisco IOS XR)

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