How severe is CVE-2021-1236?

CVE-2021-1236 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-1236 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-1236?

CVE-2021-1236 primarily affects Cisco Ios Xe. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-1236?

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

When was CVE-2021-1236 published?

CVE-2021-1236 was published on 2021-01-13 and last updated on 2026-06-17.

CVE-2021-1236

CVE-2021-1236 is a medium-severity vulnerability in Cisco Ios Xe with a CVSS 3.x base score of 5.3. 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-670.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 2% (80th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-670
Affected product: Cisco Ios Xe
Published: 2021-01-13
Last modified: 2026-06-17

Description

Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.

Frequently asked questions

What is CVE-2021-1236?: Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.
How severe is CVE-2021-1236?: CVE-2021-1236 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-1236 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-1236?: CVE-2021-1236 primarily affects Cisco Ios Xe. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-1236?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-1236 published?: CVE-2021-1236 was published on 2021-01-13 and last updated on 2026-06-17.

References

Affected products (8)

cpe:2.3:o:cisco:ios_xe:*:*:*:*:*:*:*:*
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cpe:2.3:a:cisco:secure_firewall_management_center:2.9.14.0:*:*:*:*:*:*:*
cpe:2.3:a:cisco:secure_firewall_management_center:2.9.14.14:*:*:*:*:*:*:*
cpe:2.3:a:cisco:secure_firewall_management_center:2.9.15:*:*:*:*:*:*:*
cpe:2.3:a:cisco:secure_firewall_management_center:2.9.16:*:*:*:*:*:*:*
cpe:2.3:a:cisco:secure_firewall_management_center:2.9.17:*:*:*:*:*:*:*
cpe:2.3:a:snort:snort:*:*:*:*:*:*:*:*

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