CVE-2021-40847Public exploitNetwork attack vector

Root code execution via unsigned database updates

Published Sep 21, 2021 · Updated Aug 4, 2024

Remote code execution in the Circle update service on affected NETGEAR router firmware allows man-in-the-middle attackers to run code as root. The circled daemon downloads an unsigned database archive over HTTP and extracts it beside root-run scripts, allowing crafted entries to replace executable files. An attacker must intercept and modify router traffic; exploitation grants root control even when Circle parental controls are disabled.

CVSS severity8.1
High
EPSS probability10.01%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in the Circle update service on affected NETGEAR router firmware allows man-in-the-middle attackers to run code as root. The circled daemon downloads an unsigned database archive over HTTP and extracts it beside root-run scripts, allowing crafted entries to replace executable files. An attacker must intercept and modify router traffic; exploitation grants root control even when Circle parental controls are disabled.

The record

CVE
CVE-2021-40847
Published
Sep 21, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 21, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.1NETGEARCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
9.3NIST NVDAV:N/AC:M/Au:N/C:C/I:C/A:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-319Cleartext Transmission of Sensitive Information
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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