CVE-2021-1394

mediumpriority · track · 21EPSS 0.013 · 71 %ileEURUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

1.32% (71st) EPSS

CVSS 4.3 · medium

Is it mine?

23 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · cisco_csaf

EPSS · scored 2026-10-27

A vulnerability in the ingress traffic manager of Cisco IOS XE Software for Cisco Network Convergence System (NCS) 520 Routers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the web management interface of an affected device. This vulnerability is due to incorrect processing of certain IPv4 TCP traffic that is destined to an affected device. An attacker could exploit this vulnerability by sending a large number of crafted TCP packets to the affected device. A successful exploit could allow the attacker to cause the web management interface to become unavailable, resulting in a DoS condition. Note: This vulnerability does not impact traffic that is going through the device or going to the Management Ethernet interface of the device.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

Fixed16.10.1cisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1acisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1bcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1ccisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1dcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1ecisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1fcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1gcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed16.10.1scisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.11.99SWcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com

cvss

Technical severity, 0–10. One row per scoring source.

5.3

010

base score 0–10 · higher = more severe · hover a vector to decode

v2.04.3mediumAV:N/AC:M/Au:N/C:N/I:N/A:Pprimary · NVD / NIST USexploitability 8.6 · impact 2.9

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lprimary · NVD / NIST USexploitability 3.9 · impact 1.4

v3.15.3mediumAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lsecondary · FSTEC (BDU) RU

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lsecondary · ENISA EU

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lsecondary · psirt@cisco.com USexploitability 3.9 · impact 1.4

v3.14.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:Usecondary · CVSS-BT (t0sche)

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lsecondary · Cisco PSIRT US

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: yes · Technical Impact: partialcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-399USCWE-399US

affected products (23)

Products and version ranges known to be affected.

Cisco 16.10.1all versionscisco_csafUS
Cisco 16.10.1aall versionscisco_csafUS
Cisco 16.10.1ball versionscisco_csafUS
Cisco 16.10.1call versionscisco_csafUS
Cisco 16.10.1dall versionscisco_csafUS
Cisco 16.10.1eall versionscisco_csafUS
Cisco 16.10.1fall versionscisco_csafUS
Cisco 16.10.1gall versionscisco_csafUS
Cisco 16.10.1sall versionscisco_csafUS
Cisco 17.11.99SWall versionscisco_csafUS
Cisco Cisco IOS XE Software≤ n/aenisa_euvdEU
Cisco Systems Inc. Cisco IOS XE≤ 17.2fstec_bduRU
Cisco Systems Inc. Cisco IOS XE≤ 16.1fstec_bduRU
cisco ios xe= 16.10.1nvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1anvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1bnvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1cnvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1dnvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1envdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 16.10.1fnvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*

showing 20 of 23

advisories (1)

Vendor and ecosystem advisories describing this.

cisco-sa-ncs520-tcp-ZpzzOxBCisco IOS XE Software for Network Convergence System 520 Routers Denial of Service Vulnerability2021-03-24csaf · cisco_csafUS
A vulnerability in the ingress traffic manager of Cisco IOS XE Software for Cisco Network Convergence System (NCS) 520 Routers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the web management interface of an affected device. This vulnerability is due to incorrect processing of certain IPv4 TCP traffic that is destined to an affected device. An attacker could exploit this vulnerability by sending a large number of crafted TCP packets to the affected device. A successful exploit could allow the attacker to cause the web management interface to become unavailable, resulting in a DoS condition. Note: This vulnerability does not impact traffic that is going through the device or going to the Management Ethernet interface of the device. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu cisco_csaf nvd NVD CVE.org MITRE

published 2021-03-24modified 2026-06-17

references (5)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan