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.

Published: 2021-03-29 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-27239 is rated Moderate Risk (50.7/100): CVSS High severity, with low exploitation likelihood (EPSS 0.74%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-27239

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 2.59% 0.74% -1.85%
2 2025-08-20 1.93% 2.59% +0.67%
3 2025-03-30 — 1.93% —

Full EPSS history (14 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-27239

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
8.8 3.0 HIGH
CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
8.3 2.0 HIGH
AV:A/AC:L/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:A)
Requires access to an adjacent network segment.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 6.5 10.0 [email protected]

Weakness enumeration for CVE-2021-27239

Affected software / configurations for CVE-2021-27239

Vendor Product Version Raw CPE
netgear d6220_firmware < 1.0.0.68 cpe:2.3:o:netgear:d6220_firmware:*:*:*:*:*:*:*:*
netgear d6400_firmware < 1.0.0.102 cpe:2.3:o:netgear:d6400_firmware:*:*:*:*:*:*:*:*
netgear d7000_firmware < 1.0.0.66 cpe:2.3:o:netgear:d7000_firmware:*:*:*:*:*:*:*:*
netgear d8500_firmware < 1.0.3.60 cpe:2.3:o:netgear:d8500_firmware:*:*:*:*:*:*:*:*
netgear dc112a_firmware < 1.0.0.54 cpe:2.3:o:netgear:dc112a_firmware:*:*:*:*:*:*:*:*
netgear ex7000_firmware < 1.0.1.94 cpe:2.3:o:netgear:ex7000_firmware:*:*:*:*:*:*:*:*
netgear ex7500_firmware < 1.0.0.72 cpe:2.3:o:netgear:ex7500_firmware:*:*:*:*:*:*:*:*
netgear r6250_firmware < 1.0.4.48 cpe:2.3:o:netgear:r6250_firmware:*:*:*:*:*:*:*:*
netgear r6300_firmware < 1.0.4.50 cpe:2.3:o:netgear:r6300_firmware:*:*:*:*:*:*:*:*
netgear r6400_firmware < 1.0.1.68 cpe:2.3:o:netgear:r6400_firmware:*:*:*:*:*:*:*:*
netgear r6400_firmware < 1.0.4.102 cpe:2.3:o:netgear:r6400_firmware:*:*:*:*:*:*:*:*
netgear r6700_firmware < 1.0.4.102 cpe:2.3:o:netgear:r6700_firmware:*:*:*:*:*:*:*:*
netgear r6900p_firmware < 1.3.2.132 cpe:2.3:o:netgear:r6900p_firmware:*:*:*:*:*:*:*:*
netgear r7000_firmware < 1.0.11.116 cpe:2.3:o:netgear:r7000_firmware:*:*:*:*:*:*:*:*
netgear r7000p_firmware < 1.3.2.132 cpe:2.3:o:netgear:r7000p_firmware:*:*:*:*:*:*:*:*
netgear r7100lg_firmware < 1.0.0.64 cpe:2.3:o:netgear:r7100lg_firmware:*:*:*:*:*:*:*:*
netgear r7850_firmware < 1.0.5.68 cpe:2.3:o:netgear:r7850_firmware:*:*:*:*:*:*:*:*
netgear r7900_firmware < 1.0.4.38 cpe:2.3:o:netgear:r7900_firmware:*:*:*:*:*:*:*:*
netgear r7900p_firmware < 1.4.1.68 cpe:2.3:o:netgear:r7900p_firmware:*:*:*:*:*:*:*:*
netgear r7960p_firmware < 1.4.1.68 cpe:2.3:o:netgear:r7960p_firmware:*:*:*:*:*:*:*:*
netgear r8000_firmware < 1.0.4.68 cpe:2.3:o:netgear:r8000_firmware:*:*:*:*:*:*:*:*
netgear r8000p_firmware < 1.4.1.68 cpe:2.3:o:netgear:r8000p_firmware:*:*:*:*:*:*:*:*
netgear r8300_firmware < 1.0.2.144 cpe:2.3:o:netgear:r8300_firmware:*:*:*:*:*:*:*:*
netgear r8500_firmware < 1.0.2.144 cpe:2.3:o:netgear:r8500_firmware:*:*:*:*:*:*:*:*
netgear rax200_firmware < 1.0.2.88 cpe:2.3:o:netgear:rax200_firmware:*:*:*:*:*:*:*:*
netgear rax75_firmware < 1.0.3.102 cpe:2.3:o:netgear:rax75_firmware:*:*:*:*:*:*:*:*
netgear rax80_firmware < 1.0.3.102 cpe:2.3:o:netgear:rax80_firmware:*:*:*:*:*:*:*:*
netgear rbr750_firmware < 3.2.17.12 cpe:2.3:o:netgear:rbr750_firmware:*:*:*:*:*:*:*:*
netgear rbr850_firmware < 3.2.17.12 cpe:2.3:o:netgear:rbr850_firmware:*:*:*:*:*:*:*:*
netgear rbs40v_firmware < 2.6.2.4 cpe:2.3:o:netgear:rbs40v_firmware:*:*:*:*:*:*:*:*
netgear rbs750_firmware < 3.2.17.12 cpe:2.3:o:netgear:rbs750_firmware:*:*:*:*:*:*:*:*
netgear rbs850_firmware < 3.2.17.12 cpe:2.3:o:netgear:rbs850_firmware:*:*:*:*:*:*:*:*
netgear rs400_firmware <= 1.5.0.68 cpe:2.3:o:netgear:rs400_firmware:*:*:*:*:*:*:*:*
netgear wndr3400_firmware < 1.0.1.38 cpe:2.3:o:netgear:wndr3400_firmware:*:*:*:*:*:*:*:*
netgear wnr3500l_firmware < 1.2.0.66 cpe:2.3:o:netgear:wnr3500l_firmware:*:*:*:*:*:*:*:*
netgear xr300_firmware < 1.0.3.56 cpe:2.3:o:netgear:xr300_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-27239

cvelogic Threat Intelligence