How severe is CVE-2016-4521?

CVE-2016-4521 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-2016-4521 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4521?

CVE-2016-4521 primarily affects Sixnet Bt-5 Series Cellular Router Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4521?

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-2016-4521 published?

CVE-2016-4521 was published on 2016-05-31 and last updated on 2026-06-17.

CVE-2016-4521

CVE-2016-4521 is a critical-severity vulnerability in Sixnet Bt-5 Series Cellular Router 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-200.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 2% (83rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-200
Affected product: Sixnet Bt-5 Series Cellular Router Firmware
Published: 2016-05-31
Last modified: 2026-06-17

Description

Sixnet BT-5xxx and BT-6xxx M2M devices before 3.8.21 and 3.9.x before 3.9.8 have hardcoded credentials, which allows remote attackers to obtain access via unspecified vectors.

Frequently asked questions

What is CVE-2016-4521?: Sixnet BT-5xxx and BT-6xxx M2M devices before 3.8.21 and 3.9.x before 3.9.8 have hardcoded credentials, which allows remote attackers to obtain access via unspecified vectors.
How severe is CVE-2016-4521?: CVE-2016-4521 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-2016-4521 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4521?: CVE-2016-4521 primarily affects Sixnet Bt-5 Series Cellular Router Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4521?: 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-2016-4521 published?: CVE-2016-4521 was published on 2016-05-31 and last updated on 2026-06-17.

References

https://ics-cert.us-cert.gov/advisories/ICSA-16-147-02

Affected products (2)

cpe:2.3:o:sixnet:bt-5_series_cellular_router_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:sixnet:bt-6_series_cellular_router_firmware:*:*:*:*:*:*:*:*

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