CVE-2021-20166Public exploit

Authentication bypass via overflowing CGI query buffer

Published Dec 30, 2021 · Updated Aug 3, 2024

Buffer overrun in NETGEAR Nighthawk RAX43 firmware 1.0.3.96 allows remote attackers to bypass CGI authentication via a crafted POST URL. An erroneous strlcpy() call copies an oversized query string into a 256-byte array and overwrites PATH_INFO with an attacker-controlled API path. An attacker must reach the router's LAN interface; successful exploitation redirects request handling to a designated CGI binary without authentication.

CVSS severity8.8
High
EPSS probability2.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overrun in NETGEAR Nighthawk RAX43 firmware 1.0.3.96 allows remote attackers to bypass CGI authentication via a crafted POST URL. An erroneous strlcpy() call copies an oversized query string into a 256-byte array and overwrites PATH_INFO with an attacker-controlled API path. An attacker must reach the router's LAN interface; successful exploitation redirects request handling to a designated CGI binary without authentication.

The record

CVE
CVE-2021-20166
Published
Dec 30, 2021
Updated
Aug 3, 2024
Vendor
NETGEAR
Product
Nighthawk RAX43
Classifications
CWE-120, T1190
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.0.3.96

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

NETGEAR · Nighthawk RAX43version=1.0.3.96

Published CVSS scores

5.8NIST NVDAV:A/AC:L/Au:N/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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