CVE-2021-39509Public exploitNetwork attack vector

Unauthenticated command execution via decoded username parameter

Published Aug 24, 2021 · Updated Aug 4, 2024

OS command injection in D-Link DIR-816 A2 firmware 1.10CNB05_R1B011D88210 allows remote attackers to execute commands through an HTTP request. The /goform/form2userconfig.cgi handler Base64-decodes the username parameter and incorporates the result into a shell command without neutralizing metacharacters. The published request needs a token fetched from the login page but shows no authenticated session, and injected commands execute on the router.

CVSS severity9.8
Critical
EPSS probability5.10%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in D-Link DIR-816 A2 firmware 1.10CNB05_R1B011D88210 allows remote attackers to execute commands through an HTTP request. The /goform/form2userconfig.cgi handler Base64-decodes the username parameter and incorporates the result into a shell command without neutralizing metacharacters. The published request needs a token fetched from the login page but shows no authenticated session, and injected commands execute on the router.

The record

CVE
CVE-2021-39509
Published
Aug 24, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-77, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')
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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