HOMEVULNERABILITIESCVE-2021-27256
HIGH

CVE-2021-27256

CWE-78Published: March 5, 2021· Updated: Jun 17, 2026

8.8
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-27256 requires adjacent network access, limiting remote exploitation but still posing risk in shared or local network environments.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 8.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorAdjacent
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

netgear86 product(s)
br200 firmwarebr200br500 firmwarebr500d7800 firmwared7800ex6100v2 firmwareex6100v2ex6150v2 firmwareex6150v2ex6250 firmwareex6250+74
Source: NVD CPE · 86 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

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

All References (4)

→
https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-ExtendersPatch · Vendor Advisory
→
https://www.zerodayinitiative.com/advisories/ZDI-21-262/Third Party Advisory · VDB Entry
→
https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-ExtendersPatch · Vendor Advisory
→
https://www.zerodayinitiative.com/advisories/ZDI-21-262/Third Party Advisory · VDB Entry

Quick Facts

CVE IDCVE-2021-27256
CVSS Score8.8 / 10
SeverityHIGH
WeaknessCWE-78
CISA KEVNo
Affected1 vendor(s)
PublishedMar 5, 2021

Related CVEs (CWE-78)

CVE-2024-47407
10.0
CVE-2025-64128
10.0
CVE-2024-24576
10.0
CVE-2023-3939
10.0
CVE-2024-52034
10.0
CVE-2025-64126
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-27256 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
← All Vulnerabilities·Search for CVE-2021-27256·NVD