high
7.5
CWE
476
Advisory Published
Updated

CVE-2021-34737: Cisco IOS XR Software DHCP Version 4 Server Denial of Service Vulnerability

First published: Thu Sep 09 2021(Updated: )

A vulnerability in the DHCP version 4 (DHCPv4) server feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to trigger a crash of the dhcpd process, resulting in a denial of service (DoS) condition. This vulnerability exists because certain DHCPv4 messages are improperly validated when they are processed by an affected device. An attacker could exploit this vulnerability by sending a malformed DHCPv4 message to an affected device. A successful exploit could allow the attacker to cause a NULL pointer dereference, resulting in a crash of the dhcpd process. While the dhcpd process is restarting, which may take up to approximately two minutes, DHCPv4 server services are unavailable on the affected device. This could temporarily prevent network access to clients that join the network during that time period. Note: Only the dhcpd process crashes and eventually restarts automatically. The router does not reload.

Credit: ykramarz@cisco.com

Affected SoftwareAffected VersionHow to fix
Cisco IOS XR<7.3.2
Cisco IOS XR>=7.4.0<=7.4.1
Cisco Asr 9000v-v2
Cisco Asr 9001
Cisco Asr 9006
Cisco Asr 9010
Cisco Asr 9901
Cisco Asr 9902
Cisco Asr 9903
Cisco Asr 9904
Cisco Asr 9906
Cisco Asr 9910
Cisco Asr 9912
Cisco Asr 9922
Cisco Ios Xrv 9000
Cisco IOS XR>=7.4.0<7.4.1
Cisco Ncs540-12z20g-sys-a
Cisco Ncs540-12z20g-sys-d
Cisco Ncs540-24z8q2c-m
Cisco Ncs540-24z8q2c-sys
Cisco Ncs540-28z4c-sys-a
Cisco Ncs540-28z4c-sys-d
Cisco Ncs540-acc-sys
Cisco Ncs540x-12z16g-sys-a
Cisco Ncs540x-12z16g-sys-d
Cisco Ncs540x-16z4g8q2c-a
Cisco Ncs540x-16z4g8q2c-d
Cisco Ncs540x-acc-sys
Cisco Ncs 5001
Cisco Ncs 5002
Cisco Ncs 5011
Cisco Ncs 560-4
Cisco Ncs 560-7
Cisco Ncs 5501
Cisco Ncs 5501-se
Cisco Ncs 5502
Cisco Ncs 5502-se
Cisco Ncs 5508
Cisco Ncs 5516

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Reference Links

Frequently Asked Questions

  • What is CVE-2021-34737?

    CVE-2021-34737 is a vulnerability in the DHCP version 4 (DHCPv4) server feature of Cisco IOS XR Software.

  • How does CVE-2021-34737 affect Cisco IOS XR Software?

    CVE-2021-34737 allows an unauthenticated, remote attacker to trigger a crash of the dhcpd process, resulting in a denial of service (DoS) condition.

  • What is the severity of CVE-2021-34737?

    CVE-2021-34737 has a severity rating of 7.5 (High).

  • Which versions of Cisco IOS XR Software are affected by CVE-2021-34737?

    CVE-2021-34737 affects Cisco IOS XR Software versions up to and including 7.3.2, as well as versions 7.4.0 and 7.4.1.

  • How to fix CVE-2021-34737?

    To fix CVE-2021-34737, it is recommended to upgrade to a fixed software release.

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