How severe is CVE-2015-6321?

CVE-2015-6321 has a CVSS 2.0 base score of 7.8, rated high severity.

Is CVE-2015-6321 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2015-6321?

CVE-2015-6321 primarily affects Cisco Web Security Appliance. In total, 40 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2015-6321?

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-2015-6321 published?

CVE-2015-6321 was published on 2015-11-06 and last updated on 2026-06-17.

CVE-2015-6321

CVE-2015-6321 is a high-severity vulnerability in Cisco Web Security Appliance with a CVSS 2.0 base score of 7.8. 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-399.

Key facts

Severity: High (CVSS 2.0 base score 7.8)
EPSS exploit prediction: 3% (85th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-399
Affected product: Cisco Web Security Appliance
Published: 2015-11-06
Last modified: 2026-06-17

Description

Cisco AsyncOS before 8.5.7-042, 9.x before 9.1.0-032, 9.1.x before 9.1.1-023, and 9.5.x and 9.6.x before 9.6.0-042 on Email Security Appliance (ESA) devices; before 9.1.0-032, 9.1.1 before 9.1.1-005, and 9.5.x before 9.5.0-025 on Content Security Management Appliance (SMA) devices; and before 7.7.0-725 and 8.x before 8.0.8-113 on Web Security Appliance (WSA) devices allows remote attackers to cause a denial of service (memory consumption) via a flood of TCP packets, aka Bug IDs CSCus79774, CSCus79777, and CSCzv95795.

Frequently asked questions

What is CVE-2015-6321?: Cisco AsyncOS before 8.5.7-042, 9.x before 9.1.0-032, 9.1.x before 9.1.1-023, and 9.5.x and 9.6.x before 9.6.0-042 on Email Security Appliance (ESA) devices; before 9.1.0-032, 9.1.1 before 9.1.1-005, and 9.5.x before 9.5.0-025 on Content Security Management Appliance (SMA) devices; and before 7.7.0-725 and 8.x before 8.0.8-113 on Web Security Appliance (WSA) devices allows remote attackers to cause a denial of service (memory consumption) via a flood of TCP packets, aka Bug IDs CSCus79774, CSCus79777, and CSCzv95795.
How severe is CVE-2015-6321?: CVE-2015-6321 has a CVSS 2.0 base score of 7.8, rated high severity.
Is CVE-2015-6321 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-6321?: CVE-2015-6321 primarily affects Cisco Web Security Appliance. In total, 40 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-6321?: 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-2015-6321 published?: CVE-2015-6321 was published on 2015-11-06 and last updated on 2026-06-17.

References

Affected products (40)

cpe:2.3:a:cisco:web_security_appliance:5.6.0-623:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:6.0.0-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.5.0-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.5.0-825:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.5.1-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.5.2-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.7.0-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:7.7.1-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:8.0.0-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:web_security_appliance:8.5.0.000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:7.8.0-328:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:7.8.1-001:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:7.9.0-201:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:7.9.2-116:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.0.1-031:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.1.0-001:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.1.1-033:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.1.2-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.2.0-238:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.3.0-350:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.3.5-061:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.3.6-014:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.3.7-010:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:8.4.0-150:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:9.0.0-073:*:*:*:*:*:*:*
cpe:2.3:a:cisco:content_security_management_appliance:9.1.0-004:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:7.6.1-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:7.6.3-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:7.7.0-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:7.7.1-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:7.8.0-311:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:8.5.6-052:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:8.6.0-011:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:8.9.1-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:8.9.2-032:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:9.0.0-212:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:9.0.5-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:9.1.0-011:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:9.4.4-000:*:*:*:*:*:*:*
cpe:2.3:a:cisco:email_security_appliance:9.5.0-000:*:*:*:*:*:*:*

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