How severe is CVE-2021-27256?

CVE-2021-27256 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-27256 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27256?

CVE-2021-27256 primarily affects Netgear Br200 Firmware. In total, 43 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27256?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-27256 published?

CVE-2021-27256 was published on 2021-03-05 and last updated on 2026-06-17.

CVE-2021-27256

CVE-2021-27256 is a high-severity vulnerability in Netgear Br200 Firmware with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-78.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 8.3
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-78
Affected product: Netgear Br200 Firmware
Published: 2021-03-05
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-27256?: 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.
How severe is CVE-2021-27256?: CVE-2021-27256 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27256 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27256?: CVE-2021-27256 primarily affects Netgear Br200 Firmware. In total, 43 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27256?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-27256 published?: CVE-2021-27256 was published on 2021-03-05 and last updated on 2026-06-17.

References

Affected products (43)

cpe:2.3:o:netgear:br200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:br500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:d7800_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6100v2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6150v2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6250_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6400v2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6410_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex6420_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7300v2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7320_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex8000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:lbr20_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7800_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r8900_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r9000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk12_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk13_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk14_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk15_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk20_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk23_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk40_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk43_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk43s_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk44_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbk53_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr10_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr20_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr40_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs10_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs20_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs40_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs50y_firmware:*:*:*:*:*:*:*:*

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CVE-2021-27255 — High (CVSS 8.8): This vulnerability allows remote attackers to execute arbitrary code on affected installations of NETGEAR R7800…
CVE-2021-27254 — High (CVSS 8.8): This vulnerability allows network-adjacent attackers to bypass authentication on affected installations of NETGEAR…
CVE-2021-27257 — Medium (CVSS 6.5): This vulnerability allows network-adjacent attackers to compromise the integrity of downloaded information on affected…

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