What’s Vulnerable › Vulnerabilities

CVE-2021-27256

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-05 · updated 2026-06-17
• Weakness: CWE-78

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.

Affected products

• NETGEAR Br200 Firmware: before 5.10.0.5 — fixed in 5.10.0.5
• NETGEAR Br500 Firmware: before 5.10.0.5 — fixed in 5.10.0.5
• NETGEAR D7800 Firmware: before 1.0.1.60 — fixed in 1.0.1.60
• NETGEAR Ex6100V2 Firmware: before 1.0.1.98 — fixed in 1.0.1.98
• NETGEAR Ex6150V2 Firmware: before 1.0.1.98 — fixed in 1.0.1.98
• NETGEAR Ex6250 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex6400 Firmware: before 1.0.2.158 — fixed in 1.0.2.158
• NETGEAR Ex6400V2 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex6410 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex6420 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex7300 Firmware: before 1.0.2.158 — fixed in 1.0.2.158
• NETGEAR Ex7300V2 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex7320 Firmware: before 1.0.0.134 — fixed in 1.0.0.134
• NETGEAR Ex7700 Firmware: before 1.0.0.216 — fixed in 1.0.0.216
• NETGEAR Ex8000 Firmware: before 1.0.1.232 — fixed in 1.0.1.232
• NETGEAR Lbr20 Firmware: before 2.6.3.50 — fixed in 2.6.3.50
• NETGEAR R7800 Firmware: before 1.0.2.80 — fixed in 1.0.2.80
• NETGEAR R8900 Firmware: before 1.0.5.28 — fixed in 1.0.5.28
• NETGEAR R9000 Firmware: before 1.0.5.28 — fixed in 1.0.5.28
• NETGEAR Rbk12 Firmware: before 2.7.2.104 — fixed in 2.7.2.104
• NETGEAR Rbk13 Firmware: before 2.7.2.104 — fixed in 2.7.2.104
• NETGEAR Rbk14 Firmware: before 2.7.2.104 — fixed in 2.7.2.104
• NETGEAR Rbk15 Firmware: before 2.7.2.104 — fixed in 2.7.2.104
• NETGEAR Rbk20 Firmware: before 2.6.2.104 — fixed in 2.6.2.104
• NETGEAR Rbk23 Firmware: before 2.7.2.104 — fixed in 2.7.2.104
• NETGEAR Rbk40 Firmware: before 2.6.2.104 — fixed in 2.6.2.104
• NETGEAR Rbk43 Firmware: before 2.6.2.104 — fixed in 2.6.2.104
• NETGEAR Rbk43S Firmware: before 2.6.2.104 — fixed in 2.6.2.104
• NETGEAR Rbk44 Firmware: before 2.6.2.104 — fixed in 2.6.2.104
• NETGEAR Rbk50 Firmware: before 2.7.2.104 — fixed in 2.7.2.104

How to fix

Upgrade to a fixed version: 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. Check the vendor advisory for mitigations.

References

• https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
• https://www.zerodayinitiative.com/advisories/ZDI-21-262/
• https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
• https://www.zerodayinitiative.com/advisories/ZDI-21-262/

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