Vulnerability identifier: #VU56431

Vulnerability risk: Medium

CVSSv3.1: 5.7 [CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-34737

CWE-ID: CWE-476

Exploitation vector: Local network

Exploit availability: No

Vulnerable software:
Cisco IOS XR
Operating systems & Components / Operating system
Cisco IOS XRv 9000 Router
Hardware solutions / Routers & switches, VoIP, GSM, etc
Cisco ASR 9000 Series Aggregation Services Routers
Hardware solutions / Routers & switches, VoIP, GSM, etc
NCS5000
Hardware solutions / Routers & switches, VoIP, GSM, etc
NCS540
Hardware solutions / Firmware
NCS560
Hardware solutions / Firmware
NCS5500
Hardware solutions / Firmware

Vendor: Cisco Systems, Inc

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a NULL pointer dereference error in the DHCP version 4 (DHCPv4) server feature of Cisco IOS XR Software. A remote non-authenticated attacker can send specially crafted DHCPv4 messages to the affected device, trigger a NULL pointer dereference error and crash the dhcpd process.

Mitigation
Install update from vendor's website.

Vulnerable software versions

Cisco IOS XR: 6.8 - 7.4

Cisco IOS XRv 9000 Router: All versions

Cisco ASR 9000 Series Aggregation Services Routers: 7.1 - 7.4

NCS540: All versions

NCS560: All versions

NCS5500: All versions

NCS5000: All versions

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External links
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dhcp-dos-pjPVReLU
http://bst.cloudapps.cisco.com/bugsearch/bug/CSCvw95930

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.