How severe is CVE-2021-27239?

CVE-2021-27239 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-2021-27239 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (50th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27239?

CVE-2021-27239 primarily affects Netgear D6220 Firmware. In total, 35 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27239?

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-2021-27239 published?

CVE-2021-27239 was published on 2021-03-29 and last updated on 2026-06-17.

CVE-2021-27239

CVE-2021-27239 is a high-severity vulnerability in Netgear D6220 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-121.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 8.3
EPSS exploit prediction: 1% (50th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-121
Affected product: Netgear D6220 Firmware
Published: 2021-03-29
Last modified: 2026-06-17

Description

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400 and R6700 firmware version 1.0.4.98 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the upnpd service, which listens on UDP port 1900 by default. A crafted MX header field in an SSDP message can trigger an overflow of a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-11851.

Frequently asked questions

What is CVE-2021-27239?: This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400 and R6700 firmware version 1.0.4.98 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the upnpd service, which listens on UDP port 1900 by default. A crafted MX header field in an SSDP message can trigger an overflow of a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-11851.
How severe is CVE-2021-27239?: CVE-2021-27239 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-2021-27239 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (50th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27239?: CVE-2021-27239 primarily affects Netgear D6220 Firmware. In total, 35 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27239?: 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-2021-27239 published?: CVE-2021-27239 was published on 2021-03-29 and last updated on 2026-06-17.

References

Affected products (35)

cpe:2.3:o:netgear:d6220_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:d6400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:d7000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:d8500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:dc112a_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:ex7500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r6250_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r6300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r6400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r6700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r6900p_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7000p_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7100lg_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7850_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7900_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7900p_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r7960p_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r8000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r8000p_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r8300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:r8500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rax200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rax75_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rax80_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr750_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbr850_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs40v_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs750_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rbs850_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:rs400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:wndr3400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:wnr3500l_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:netgear:xr300_firmware:*:*:*:*:*:*:*:*

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