PatchTheCVECVE-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
CVE-2016-4521 is a critical-severity flaw (CVSS 9.8) affecting bt-5 series cellular router firmware, bt-6 series cellular router firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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.
Why this priority
- Critical severity
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.8 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 2.5% (top 16%) |
| CISA exploited list | No |
| Weakness | CWE-200 |
| Published | 2016-05-31 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2016-4521?
bt-5 series cellular router firmware: upgrade to newer than 3.9.7; bt-6 series cellular router firmware: upgrade to newer than 3.9.7. Exact commands for each OS are on this page.
Is CVE-2016-4521 being exploited?
CVE-2016-4521 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2016-4521 affect?
CVE-2016-4521 affects bt-5 series cellular router firmware, bt-6 series cellular router firmware. Severity is critical (CVSS 9.8). 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 urgent is CVE-2016-4521?
Priority 60/100. Critical severity; Remotely exploitable, no login, no user action