Cisco IOS XE Software Web UI Denial of Service Vulnerabilities

published 2021-03-24 5y ago modified 2026-06-17 4mo ago also EUVD-2021-6823

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.0%; EPSS 1.0% chance of exploitation in 30 days, percentile 62%
public exploits: 0; none known

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.

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CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2y ago (2024-11-08)

Exploit prediction

0.98% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
NVD	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
NVD	2.0	3.5	AV:N/AC:M/Au:S/C:N/I:N/A:P

Affected products

Cisco Cisco IOS XE Software

Classification

Weakness

CWE-20 Improper Input Validation
CWE-755 Improper Handling of Exceptional Conditions

Technology feeds

Cisco IOS rss critical rss

References

tools.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-webui-dos-z9yqYQAn
vendor-advisory

Sources

CVE List CVE-2021-1356
NVD CVE-2021-1356

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