How severe is CVE-2016-6406?

CVE-2016-6406 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2016-6406 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (88th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-6406?

CVE-2016-6406 primarily affects Cisco Email Security Appliance Firmware. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-6406?

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

When was CVE-2016-6406 published?

CVE-2016-6406 was published on 2016-09-22 and last updated on 2026-06-17.

CVE-2016-6406

CVE-2016-6406 is a critical-severity vulnerability in Cisco Email Security Appliance Firmware with a CVSS 3.x base score of 9.8. 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-264.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 4% (88th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-264
Affected product: Cisco Email Security Appliance Firmware
Published: 2016-09-22
Last modified: 2026-06-17

Description

Cisco IronPort AsyncOS 9.1.2-023, 9.1.2-028, 9.1.2-036, 9.7.2-046, 9.7.2-047, 9.7.2-054, 10.0.0-124, and 10.0.0-125 on Email Security Appliance (ESA) devices, when Enrollment Client before 1.0.2-065 is installed, allows remote attackers to obtain root access via a connection to the testing/debugging interface, aka Bug ID CSCvb26017.

Frequently asked questions

What is CVE-2016-6406?: Cisco IronPort AsyncOS 9.1.2-023, 9.1.2-028, 9.1.2-036, 9.7.2-046, 9.7.2-047, 9.7.2-054, 10.0.0-124, and 10.0.0-125 on Email Security Appliance (ESA) devices, when Enrollment Client before 1.0.2-065 is installed, allows remote attackers to obtain root access via a connection to the testing/debugging interface, aka Bug ID CSCvb26017.
How severe is CVE-2016-6406?: CVE-2016-6406 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2016-6406 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (88th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-6406?: CVE-2016-6406 primarily affects Cisco Email Security Appliance Firmware. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-6406?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2016-6406 published?: CVE-2016-6406 was published on 2016-09-22 and last updated on 2026-06-17.

References

Affected products (8)

cpe:2.3:o:cisco:email_security_appliance_firmware:9.1.2-023:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:9.1.2-028:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:9.1.2-036:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:9.7.2-046:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:9.7.2-047:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:9.7.2-054:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:10.0.0-124:*:*:*:*:*:*:*
cpe:2.3:o:cisco:email_security_appliance_firmware:10.0.0-125:*:*:*:*:*:*:*

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