How severe is CVE-2021-1620?

CVE-2021-1620 has a CVSS 3.x base score of 7.7, rated high 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 high.

Is CVE-2021-1620 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-1620?

CVE-2021-1620 primarily affects Cisco Ios. In total, 689 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-1620?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-1620 published?

CVE-2021-1620 was published on 2021-09-23 and last updated on 2026-06-17.

CVE-2021-1620

CVE-2021-1620 is a high-severity vulnerability in Cisco Ios with a CVSS 3.x base score of 7.7. 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-772.

Key facts

Severity: High (CVSS 3.x base score 7.7)
CVSS v2: 3.5
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-772
Affected product: Cisco Ios
Published: 2021-09-23
Last modified: 2026-06-17

Description

A vulnerability in the Internet Key Exchange Version 2 (IKEv2) support for the AutoReconnect feature of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to exhaust the free IP addresses from the assigned local pool. This vulnerability occurs because the code does not release the allocated IP address under certain failure conditions. An attacker could exploit this vulnerability by trying to connect to the device with a non-AnyConnect client. A successful exploit could allow the attacker to exhaust the IP addresses from the assigned local pool, which prevents users from logging in and leads to a denial of service (DoS) condition.

Frequently asked questions

What is CVE-2021-1620?: A vulnerability in the Internet Key Exchange Version 2 (IKEv2) support for the AutoReconnect feature of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to exhaust the free IP addresses from the assigned local pool. This vulnerability occurs because the code does not release the allocated IP address under certain failure conditions. An attacker could exploit this vulnerability by trying to connect to the device with a non-AnyConnect client. A successful exploit could allow the attacker to exhaust the IP addresses from the assigned local pool, which prevents users from logging in and leads to a denial of service (DoS) condition.
How severe is CVE-2021-1620?: CVE-2021-1620 has a CVSS 3.x base score of 7.7, rated high 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 high.
Is CVE-2021-1620 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-1620?: CVE-2021-1620 primarily affects Cisco Ios. In total, 689 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-1620?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-1620 published?: CVE-2021-1620 was published on 2021-09-23 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ikev2-ebFrwMPr

Affected products (689)

cpe:2.3:o:cisco:ios:12.2\(6\)i1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svr1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svr2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svr3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svs:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svs1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svt1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svt2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.1\(3\)svu1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(1\)sy8:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e5a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e8:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e9:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e10:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e10a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)e10b:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea8:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:15.2\(4\)ea9:*:*:*:*:*:*:*

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