CVE-2021-1356

lowpriority · track · 17EPSS 0.010 · 62 %ileEURUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.98% (62nd) EPSS

CVSS 3.5 · low

Is it mine?

30 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · cisco_csaf

EPSS · scored 2026-10-27

Multiple vulnerabilities in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker with read-only privileges to cause the web UI software to become unresponsive and consume vty line instances, resulting in a denial of service (DoS) condition. These vulnerabilities are due to insufficient error handling in the web UI. An attacker could exploit these vulnerabilities by sending crafted HTTP packets to an affected device. A successful exploit could allow the attacker to cause the web UI software to become unresponsive and consume all available vty lines, preventing new session establishment and resulting in a DoS condition. Manual intervention would be required to regain web UI and vty session functionality. Note: These vulnerabilities do not affect the console connection.

remediations

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

A vendor fix is available.

Fixed17.1.1cisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.1.1acisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.1.1scisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.1.1tcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.1.2cisco_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
Fixed17.2.1cisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.2.1acisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.2.1rcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.2.1vcisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
Fixed17.2.2cisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com

cvss

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

4.3

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · low–medium · 3.5–4.3

v2.03.5lowAV:N/AC:M/Au:S/C:N/I:N/A:Pprimary · NVD / NIST USexploitability 6.8 · impact 2.9

v3.14.3mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:Lprimary · NVD / NIST USexploitability 2.8 · impact 1.4

v3.14.3mediumAV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:Lsecondary · FSTEC (BDU) RU

v3.14.3mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:Lsecondary · ENISA EU

v3.14.3mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:Lsecondary · psirt@cisco.com USexploitability 2.8 · impact 1.4

v3.14mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L/E:Usecondary · CVSS-BT (t0sche)

v3.14.3mediumCVSS:3.1/AV:N/AC:L/PR:L/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.

Trackcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-755USprimaryCWE-20USCWE-20US

affected products (30)

Products and version ranges known to be affected.

Cisco 17.1.1all versionscisco_csafUS
Cisco 17.1.1aall versionscisco_csafUS
Cisco 17.1.1sall versionscisco_csafUS
Cisco 17.1.1tall versionscisco_csafUS
Cisco 17.1.2all versionscisco_csafUS
Cisco 17.11.99SWall versionscisco_csafUS
Cisco 17.2.1all versionscisco_csafUS
Cisco 17.2.1aall versionscisco_csafUS
Cisco 17.2.1rall versionscisco_csafUS
Cisco 17.2.1vall versionscisco_csafUS
Cisco 17.2.2all versionscisco_csafUS
Cisco Cisco IOS XE Software≤ n/aenisa_euvdEU
Cisco Systems Inc. Cisco IOS XE≤ 16.11fstec_bduRU
Cisco Systems Inc. Cisco IOS XE≤ 17.1fstec_bduRU
Cisco Systems Inc. Cisco IOS XE≤ 16.12fstec_bduRU
Cisco Systems Inc. Cisco IOS XE≤ 17.2fstec_bduRU
Cisco Systems Inc. Cisco IOS XE≤ 3.15Sfstec_bduRU
cisco ios xe= 17.1.1nvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 17.1.1anvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cisco ios xe= 17.1.1snvdUScpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*

showing 20 of 30

advisories (1)

Vendor and ecosystem advisories describing this.

cisco-sa-xe-webui-dos-z9yqYQAnCisco IOS XE Software Web UI Denial of Service Vulnerabilities2021-03-24csaf · cisco_csafUS
Multiple vulnerabilities in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker with read-only privileges to cause the web UI software to become unresponsive and consume vty line instances, resulting in a denial of service (DoS) condition. These vulnerabilities are due to insufficient error handling in the web UI. An attacker could exploit these vulnerabilities by sending crafted HTTP packets to an affected device. A successful exploit could allow the attacker to cause the web UI software to become unresponsive and consume all available vty lines, preventing new session establishment and resulting in a DoS condition. Manual intervention would be required to regain web UI and vty session functionality. Note: These vulnerabilities do not affect the console connection. Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.

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

related (705)

Related entries.

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+700 more

references (6)

External citations — patches, advisories, analysis.

scry

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