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Fencer Vulns
high 8.1

CVE-2021-40847 in the critical feed json

The update process of the Circle Parental Control Service on various NETGEAR routers allows remote attackers to achieve remote code executi…

published 2021-09-21 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-28003

cvss
8.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
10.0%
EPSS 10.0% chance of exploitation in 30 days, percentile 95%
public exploits
0
none known

Summary

The update process of the Circle Parental Control Service on various NETGEAR routers allows remote attackers to achieve remote code execution as root via a MitM attack. While the parental controls themselves are not enabled by default on the routers, the Circle update daemon, circled, is enabled by default. This daemon connects to Circle and NETGEAR to obtain version information and updates to the circled daemon and its filtering database. However, database updates from NETGEAR are unsigned and downloaded via cleartext HTTP. As such, an attacker with the ability to perform a MitM attack on the device can respond to circled update requests with a crafted, compressed database file, the extraction of which gives the attacker the ability to overwrite executable files with attacker-controlled code. This affects R6400v2 1.0.4.106, R6700 1.0.2.16, R6700v3 1.0.4.106, R6900 1.0.2.16, R6900P 1.3.2.134, R7000 1.0.11.123, R7000P 1.3.2.134, R7850 1.0.5.68, R7900 1.0.4.38, R8000 1.0.4.68, and RS400 1.5.0.68.

Exploit prediction

10.01% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • blog.grimm-co.com https://blog.grimm-co.com/2021/09/mama-always-told-me-not-to-trust.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C

Classification

Weakness
  • CWE-319 Cleartext Transmission of Sensitive Information

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.