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. 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-iosxr-dhcp-dos-pjPVReLU This advisory is part of the September 2021 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Cisco IOS XR Software Security Advisory Bundled Publication.
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.
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-iosxr-dhcp-dos-pjPVReLU
This advisory is part of the September 2021 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Cisco IOS XR Software Security Advisory Bundled Publication.
At the time of publication, this vulnerability affected the following Cisco products if they were running Cisco IOS XR Software releases 6.7.2 and later, 7.1.2 and later, or 7.2.1 and later but earlier than Release 7.3.2 or earlier than Release 7.4.1 and had the DHCPv4 server feature or the DHCPv4 proxy feature enabled:
See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
To determine whether the DHCPv4 server feature or the DHCPv4 proxy feature is enabled on a device, run the show running-config dhcp ipv4 command in privileged EXEC mode on the device CLI and check for a server profile that is either directly or indirectly (through a base profile) bound to at least one interface.
The following example shows the output of the show running-config dhcp ipv4 command on a device that has the DHCPv4 server profile TEST directly bound to interface GigabitEthernet0/0/0/0:
dhcp ipv4
profile TEST server
.
.
.
!
interface GigabitEthernet0/0/0/0 server profile TEST
The following example shows the output of the show running-config dhcp ipv4 command on a device that has the DHCPv4 server profiles DHCP_SERVER and DEFAULT_PROFILE indirectly bound to interface GigabitEthernet0/0/0/0 through base profile DHCP_BASE:
dhcp ipv4
profile DHCP_BASE base
match option 60 41424355 profile DHCP_SERVER server
default profile DEFAULT_PROFILE server
.
.
.
!
profile DHCP_SERVER server
.
.
.
!
profile DEFAULT_PROFILE server
.
.
.
!
interface GigabitEthernet0/0/0/0 base profile DHCP_BASE
The following example shows the output of the show running-config dhcp ipv4 command on a device that has the DHCPv4 proxy profile PROXY directly bound to interface GigabitEthernet0/0/0/0:
dhcp ipv4
profile PROXY proxy
helper-address vrf default 192.168.23.7 giaddr 192.168.23.11
!
interface GigabitEthernet0/0/0/0 proxy profile PROXY
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following Cisco products:
There are no workarounds that address this vulnerability.
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.
At the time of publication, the following Cisco IOS XR Software releases contained the fix for this vulnerability:
Cisco has released the following SMU to address this vulnerability. Customers who require SMUs for platforms or releases that are not listed are advised to contact their support organization.
| Cisco IOS XR Software Release | Platform | SMU Name |
|---|---|---|
| 7.1.3 | ASR9K-X64 | asr9k-x64-7.1.3.CSCvw95930 |
See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information, including SMU availability.
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 |
|---|---|---|---|---|
| 1.1 | Clarified vulnerable releases. | Vulnerable Products | Final | 2021-OCT-20 |
| 1.0 | Initial public release. | - | Final | 2021-SEP-08 |
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