CVE-2021-43517: FOSCAM Camera FI9805E with firmware V4.02.R12.00018510.10012.143900.00000 contains a backdoor that opens Telne

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CRITICAL 9.8REMOTEMITIGATE

CVE-2021-43517 is a critical-severity flaw (CVSS 9.8) affecting fi9805e firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

FOSCAM Camera FI9805E with firmware V4.02.R12.00018510.10012.143900.00000 contains a backdoor that opens Telnet port when special command is sent on port 9530.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Published	2022-04-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: foscam

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-04-08 17:15 UTCPublished CVE record published
2026-06-17 04:11 UTCUpdated Record last modified

foscam fi9805e firmware MITIGATE

Affected: 4.02.r12.00018510.10012.143900.00000

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.02.r12.00018510.10012.143900.00000

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
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-2021-43517?

fi9805e firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-43517 being exploited?

CVE-2021-43517 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-2021-43517 affect?

CVE-2021-43517 affects fi9805e firmware. Severity is critical (CVSS 9.8). FOSCAM Camera FI9805E with firmware V4.02.R12.00018510.10012.143900.00000 contains a backdoor that opens Telnet port when special command is sent on port 9530.

How urgent is CVE-2021-43517?

Priority 64/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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