How severe is CVE-2021-1356?

CVE-2021-1356 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2021-1356 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-1356?

CVE-2021-1356 primarily affects Cisco Ios Xe. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-1356?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-1356 published?

CVE-2021-1356 was published on 2021-03-24 and last updated on 2026-06-17.

CVE-2021-1356

CVE-2021-1356 is a medium-severity vulnerability in Cisco Ios Xe with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-755.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 3.5
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-755
Affected product: Cisco Ios Xe
Published: 2021-03-24
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-1356?: 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.
How severe is CVE-2021-1356?: CVE-2021-1356 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2021-1356 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-1356?: CVE-2021-1356 primarily affects Cisco Ios Xe. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-1356?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-1356 published?: CVE-2021-1356 was published on 2021-03-24 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-webui-dos-z9yqYQAn

Affected products (13)

cpe:2.3:o:cisco:ios_xe:3.15.1xbs:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:3.15.2xbs:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.1.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.1.1a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.1.1s:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.1.1t:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.1.2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.1a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.1r:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.1v:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:17.2.3:*:*:*:*:*:*:*

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