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Fencer Vulns
high 8.8

CVE-2021-27256 json

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R7800 firmware version…

published 2021-03-05 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-14021

cvss
8.8
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 61%
public exploits
0
none known

Summary

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R7800 firmware version 1.0.2.76. Although authentication is required to exploit this vulnerability, the existing authentication mechanism can be bypassed. The specific flaw exists within the handling of the rc_service parameter provided to apply_save.cgi. The issue results from the lack of proper validation of a user-supplied string before using it to execute a system call. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-12355.

Patch / fix

  • netgear br200_firmware 5.10.0.5
  • netgear br500_firmware 5.10.0.5
  • netgear d7800_firmware 1.0.1.60
  • netgear ex6100v2_firmware 1.0.1.98
  • netgear ex6150v2_firmware 1.0.1.98
  • netgear ex6250_firmware 1.0.0.134
  • netgear ex6400_firmware 1.0.2.158
  • netgear ex6400v2_firmware 1.0.0.134
  • netgear ex6410_firmware 1.0.0.134
  • netgear ex6420_firmware 1.0.0.134
  • netgear ex7300_firmware 1.0.2.158
  • netgear ex7300v2_firmware 1.0.0.134
  • netgear ex7320_firmware 1.0.0.134
  • netgear ex7700_firmware 1.0.0.216
  • netgear ex8000_firmware 1.0.1.232
  • netgear lbr20_firmware 2.6.3.50
  • netgear r7800_firmware 1.0.2.80
  • netgear r8900_firmware 1.0.5.28
  • netgear r9000_firmware 1.0.5.28
  • netgear rbk12_firmware 2.7.2.104

Exploit prediction

0.96% chance of exploitation in the next 30 days, higher than 61% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.0 8.8 CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 8.8 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 8.3 AV:A/AC:L/Au:N/C:C/I:C/A:C

Affected products

  • NETGEAR R7800

Classification

Weakness
  • CWE-78 Improper Neutralization of Special Elements used in an OS Command

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.